I've been playing this game a lot recently with the subreddit discord (a great community IMO) and wanted to talk about a lot of the mistakes I see people make regularly.

I will note here that for the sake of these suggestions, I have a couple assumptions:
1. I'm assuming you're in voice communication with the other players during meetings. The game plays very different between text-only and voice communications. The lack of ability to communicate well in text-only game play makes winning far more random.
2. I'm assuming you're playing in 10 player lobbies with two impostors.
3. I'm assuming you have general knowledge about when it's good/bad to vote based on player numbers.

Impostor Mistakes

I wanted to talk about impostor mistakes because I believe new/inexperienced impostors make a lot of the same mistakes. Similarly, as crew you should be looking out for these mistakes.

Beginner impostor mistakes

1. Not paying attention to who is around you. Many impostors lose because they get caught doing a kill because they didn't think that the person they just passed might turn around.
2. Not paying attention to common tasks. First, you need to know if you can get away with faking things like wires. Second, many players will ask people about common tasks, and it's important to know what those tasks are.
3. Never faking tasks. This is the #1 thing I see many new impostors do. If I cross paths with you multiple times and you're never doing a task or even appear to be going to a task, I'd say around 75% of the time you're an impostor. Faking tasks builds trust with crew and gives you a "real" story to tell when people ask you your path/tasks.
4. Running around the map too much. This is typically what impostors that are never faking tasks are doing. They're constantly running around the map and they're not doing anything a crewmate would be doing (looking for bodies, gathering info, doing tasks). Not only that, but running around too much often puts you near bodies (some of which might be kills by your impostor teammate) and leaves you with no alibi.
5. Calling non-door sabotages while dead. When your the only impostor, you really have to time your active sabotages perfectly. I've seen many impostors fail because they couldn't make plans on using the sabotages because their ghost partner was using them.
6. Not using door sabotages, especially while dead. You can drastically reduce the crews ability to search for bodies by using doors. It gives your impostor teammate time to build alibis.
7. Not reporting your teammate impostors kills. I've seen many impostors stumble across a kill their teammate made, freeze and/or try to run past only to get caught and blamed for it. Not reporting a body makes you an impostor whether or not you did the kill.

Intermediate impostor mistakes

1. Staying silent/providing no information. There's a few reasons why impostors often do this, but commonly it's because it gives crew time to sus each other or not enough time to sus you. This can be your downfall though, as this sometimes means crew will figure out that you're the only one without much of an alibi without you even saying a word. It also builds you no trust going into later rounds.
2. Not thinking about who you should or should not kill. Should kill: players who have been hard cleared, players who suspect you, particularly skillful/logical crewmates. Should not kill: crewmates who are heavily sussed or were paired with an impostor as "has to be one of the two", the only player(s) not apart of cleared groups.
3. Not continuing your own crew story. If you get asked what you were doing and answer that you were doing asteroids, and the following round RUN RIGHT PAST WEAPONS without doing them, some players will catch on.
4. Playing too fast or slow. Playing too fast is generally killing on cooldown. The problem here is that often times early on in rounds people are together, and you can end up with groups of people who are cleared because they never had time to split up. Playing too slow is much more rare to see, but the biggest problem with playing slow is that crew who are done on tasks will start to stick either on information gathering tools or group up with each other… which leaves you little to no ability to kill anyway.
5. Playing crew and impostor differently. If you normally speedrun tasks as crew, suddenly spending all round on admin will look sus. Similarly, if you normally throw sus as crew, sitting silent as impostor can be obvious. Some people don't catch onto this, but I've definitely caught onto this before with some otherwise strong players. Obviously, this only matters if you're playing with the same group over and over again.

Advanced Impostor tips

1. Provide fake information if you can. If you're the only one on or near an information gathering tool then you have a golden opportunity to lie. With admin information you can place an extra person in a location to help clear sus from your impostor teammate. With vitals information you can make a body newer or older than it is. With camera information you can place your teammate impostor in another location or throw sus at a player without an alibi.
2. Big plays at the right time can win. Most people know not to use their teammate impostor as an alibi for multiple rounds… but some people take that to the extent of NEVER using their teammate as an alibi. This can create scenarios where you're the only ones unaccounted for and you get blame. But if there are three groups of two players all vouching for each other left, then it's much harder to know who is right. In general, I think of "making a big play" as doing a hard accuse when the outcome of the vote can determine the game (voting on 5/6 with two impostors, or voting on 3/4 with one impostor). It's worth noting that a hard accuse doesn't have to be a kill, it can be a vent accusation.
3. Be willing to throw your impostor teammate away or take the blame if you need to. Your impostor teammate is your team, you win if they win and they win if you win. If anonymous voting is off, you should be willing to vote your teammate impostor out. Similarly, if you get caught near a body – even if it wasn't yours – don't call out your other impostor if they are clear of sus.
4. Play like you are a crewmate. Most of the "mistakes" I've listed above boil down to one thing: playing like an impostor and not like crew. If you play like you are crew, then you'll have a story (tasks you faked), you'll have information to use in meetings, you won't have to scramble nearly as hard to come up with a plausible story, and you'll likely build trust with crew. So, if you play like a crew, how do you get kills? You only need to play as crew around other crew. Use your tools (sabotages) to create times where you can do things out of sight of crew. The best time to play like a crew is when your kill is on cooldown. You can't do anything anyway, might as well be getting an alibi.
5. Keep track of who to sus. Use information you have to throw sus. Part of playing like crew is trying to find out the impostors – if you aren't trying to find an impostor, you probably are an impostor, so you want to think about who you would suspect with the information you have.
6. Offer information up EARLY. If you're in an area and know others can place you there, be one of the first to call out that you were in the area and instead place OTHERS in the area as well. It's more suspicious to have others call you out than it is to call out others.
7. Similarly, if you're caught doing a kill, try to be the first to speak. People are naturally more inclined to believe the first story they hear. Also, have a story which explains why you caught the other person red handed. People are less likely to believe "I saw Red kill" than they are "Lol Red, you didn't realize I was around the corner, did you? You should have checked inside electrical before doing that kill".

Crewmate mistakes

Beginner crew mistakes

1. Not checking for bodies. I've seen people walk past rooms with bodies in them many times. It generally takes no more than 1 second to peak into a room and see if the report button lights up. It's always worth doing because the earlier a body gets found the more likely it is you'll be able to find the impostor that did it and/or clear those who couldn't have.
2. Forgetting about previous rounds. I've seen countless times "this kill HAS to be cyan or orange" – next round orange is dead and no one calls out cyan. Or it gets to last three in meeting and people forget that one person is cleared or another was sussed in every previous round. Another example of this is not following up on 50-50's. 50-50's, for those unaware, are when two players are hard accusing each other of being the impostor (typically "I saw them kill"). A lot of people will say to 50-50 them – kick out both so you can guarantee an impostor is out (which is always worth it for crew). The problem, of course, is if you kick out one of them and don't kick out the other, then you end up potentially giving the impostors a free kill (and can dangerously leave one impostor effectively "cleared").
3. Clearing people too easily. Just because you were with someone 80% of the round doesn't mean they didn't use that 20% to get a kill. Similarly, clearing someone for doing a task which you can't fully verify. I've seen impostors come in at the end of a group doing medbay scans and fake being the last – and suddenly they're hard cleared for the rest of the game by someone who couldn't verify they did it.

Intermediate crew mistakes

1. Taking focus away from gathering information related to the body found. I've seen multiple rounds where someone reports a body in admin, only to have one player on the other side of the map ask another player why they were moving weird… leading into half (or more) of the meeting time being lost to bickering over whether or not their movement made sense instead of finding out useful information (like who is near the body, who is accounted for, ect). If you have sus on someone because of something unrelated to a kill either keep it to yourself OR wait until you've already got enough relevant info about the kill that did happen. Another option is to call an emergency meeting to discuss it further. But honestly some people get frustrated over this too.
2. Only asking about current positions. It's easy to ask everyone where they are… and much easier to lie about. Impostors can give their location last and be confident that they put themselves somewhere safe but away from the body. If they have to give their pathing, though, it gets much harder to give a pathing where someone wouldn't have seen them running past.
3. Not voting together as crew. Not voting someone out when you have to is a guaranteed loss. Not voting and letting impostors control the vote is a guaranteed loss. Voting someone out, when you have to (by number of alive players), is a necessity. Because of that, you need to make sure that you vote, and you vote as a group. If you can identify someone you believe is crew either ask them who they voted for and vote the same person, OR tell them you trust them and that they should vote for someone specific.
4. Waiting until the last second to figure out who you are voting for, and not saying who it is. This is piling onto the previous mistake I mentioned. If at 15-20 seconds remaining no one in particular is obvious to vote for, you need to cut off the conversation and lead it towards voting. Pay attention to how much time in remaining! You need to vote together.
5. Not using information gathering tools, and not using providing that information. Tools like admin table, cameras, vitals are made to provide extra information. That information can often make or break people's stories. Even if it seems like it's irrelevant to you, being able to say something like "I saw three people in electric on admin table when the body was reported" can be enough to give crucial information to someone else.
6. Assuming that the only people around you when lights are off are the people you know about. I've seen many impostors win with drive-by kills while lights are off. They see a group of three people near each other while they can't be seen, get a kill and get out without being seen and the alive crew immediately blame each other since they saw no one else around.
7. Voting too early. Remember the point about voting together? If you vote early, you sacrifice your ability to vote as a group. There's no telling what other information others have, you need to hear it.

Advanced crew tips

1. When it comes to voting, sometimes the best call is to not vote on the 50-50, even when you HAVE to vote someone out. For instance: 5 players left, two are impostors. Two players hard accuse each other of killing in front of them. You as crew, believe another player (not among the 50-50) is crew (maybe due to a previous clear, or they were with you in the round, ect). In this scenario: you know one of the two in the 50-50 is crew, and one is impostor. You know you are crew, and you believe another is crew. That means the other player (not in the 50-50, and not the one you trust) has to be an impostor. You should vote THAT person out instead of taking a risk that you vote the 50-50 wrong. This is also one of the main reasons why voting early is bad as crew.
2. Not thinking into the route/tasks someone is saying. For instance, from one of my previous games, an impostor tried to avoid saying they went into lab (on polus) by saying their path was vitals -> storage -> weapons. Okay, fine. Except there is zero reason to simply stop by storage, unless you're doing fuel, in which case you wouldn't just be walking past storage. Taking a second to analyze the story and see why it doesn't make sense can be super important. This can also be really important because you'll get info about what tasks they did, and in later rounds you might catch them repeating tasks. For instance, I've seen some impostors that prefer killing in certain areas of the map go into a certain part of the map repeatedly… which doesn't make sense. Similarly, there's no reason for someone to blatantly skip a convenient opportunity to do the second part of a task that they've claimed to do the first part of. Like, if someone said they did download in electric, and then walks by comms repeatedly without going in… why?
3. If you really sus someone, or have no clue who to vote, ask the person you suspect most who they think the impostor is. It can be an incredibly revealing question, because impostors often aren't spending time thinking about who they would suspect, and crew often do. Credit to Hafu here for being the streamer I first heard suggest to ask this question.

My last tip: watch some of the regular streamers with this game. It's a lot of fun and they're great to learn from. I really enjoy Hafu and the group she often plays with (5up, jorbs, dumbdog, dakotaz, trainwrecks, talia mar… and a lot others – sorry to those I've left out, there are a lot). I'd love to hear about other streamers people find good to learn from.

I hope this helps some players. I'd also love for others to contribute some more tips, or tell me why my tips are wrong.