Since I'm seeing people doing the same mistakes over and over again in onslaught, I thought I could make a writeup summarising what I've learned so far. If only a single person reads this and learns something new and applies it, I'm happy.
1: Pick tanks that are good. The only two non heavy tanks you should consider are the cs63 for speed and map control and the tvp for flanking maneuvers. Other than that, play heavies and heavy TDs only, I don't think there's a reason to play anything other than the super conqueror, the obj. 277 and the maus. If you know what you're doing, the strv 103b might be fine too, but I haven't met a single person yet that made it work. Lights are a big no no. If you don't have any decent tier 10 tanks and still wanna play, I'd recommend playing the BZ-75 you get for this mode.
2: If your team picks bad tanks, try to make the most of it. You can't do shit if people choose to play the FV4008 or the manticore, so just try to roll with it as good as possible. Play defensive to try and involve sniper TDs, play a super heavy tank to cover for lights and wait until they eventually can flank.
3: Winning > everything else. You only gain points if you win. You always lose points if you lose. So try to get a mindset where you do your best to contribute everything to win. You can throw your tank in the way of pushing enemies so they can't decap in time? Do it, even if you die for it. You can cap through, even if you dealt 0 damage all game and will finish last of your team? Do it regardless, +16 rating is still better than a potential -40.
4: Stay as a group. If you stray off your team and get caught, you'll just die for free. Never go anywhere where your team won't be able to help you. This is especially a problem on sand river, where some meds go to the dunes and the other to the centre quite often. Both sides are fine and can be played, just make sure to focus on one so you don't split your team up completely.
5: Capping is your friend. Honestly, in lower ranks you can win half your games if just three people from your team beline to the cap and start capping right away. Most enemies will only realise what's going on once its too late. On maps like cliffs or overlord this works best, since oftenly the entire enemy team will be completely out of position and has to rush back, so you can either just farm them or keep a low profile and cap through.
6: Large parts of most maps are irrelevant. Don't go there, ever. You'll just be too far away to help your team so they'll be a man down. Irrelevant parts include the canyon and medium area of Westfield, the debris piles on pilsen, the mountain area on sand river, the little mountain path on glacier, the village on mines and most importantly the hill on himmelsdorf. I'm also not a friend if people drive to the lowest area of cliffs, but iirc there's an artillery cap there and you can reach the infamous donut quickly, so if you're fast you can probably go there (although if you're fast I'd always recommend just going on the hill instead).
7: If you're more, push, if you're less, defend. Pretty self explanatory imo, but very often I have like a 2v1 situation and push only to find out my teammate doesn't help. If you can take someone out withour losing someone yourself, it's a huge asset and might already be enough to win.
If any of you got any more tips, feel free to share them in the comments.
Source: https://www.reddit.com/r/WorldofTanks/comments/16kla25/some_tips_for_onslaught/