An easy way to find out who the impostors are is to look at admin, and if you see 2 people in cafeteria (or storage and balcony), go there immediately. One of them is probably dead, even if admin doesn't flash (dead bodies from that round are shown on admin.) The impostor probably won't expect anyone to go back there later in the round, since people usually just do any tasks they have there at the start of the round, no sabotages are fixed there, and it doesn't lead to any other parts of the map, except for storage and balcony (which both only have a couple tasks, but lot of kills take place there) so you'll probably have a good shot at seeing them before they vent. If you see 3 people there, there might be a kill, but in that case you have someone else to report it. If there's 4 people, it's probably fine, but there could be a double kill.
If you're impostor, to not get yourself seen, try to kill near the vent on balcony, since that's an easy way to not get seen after the kill. (The vent north of there won't work since you're likely to get seen venting is someone is coming.
TL;DR: look at admin, and if you see 2 people in cafe/storage/balcony, go there, since you could have a chance at finding it, since they don't expect anyone coming. If you're impostor, kill closer to balcony at vent there to not get caught.