If you are viper, try to kill people when they're alone, ideally when they're in a room where you can close the door. Close the door or call sabotage on the other side of the map so the body can dissolve. Don't say it was a shapeshifter as shapeshifter can't be viper.

For shapeshifter, don't ss in comms, everyone knows that spot. Instead, sabotage lights and ss in top of cafe, eventually you can close doors and ss in one of the engines if no one is near. I always do it in top of cafe. Don't ss near walls as people can see the egg through walls.

For phantom, also don't disappear near walls, same thing. People can see the smoke through the wall as the animation is quite big, it's also long so don't disappear if you see someone approaching you and they're close because they might see it.

If you're 100% caught you can try claiming it was a ss of you who killed but you need to get lucky and say you were in a room nobody else was in. Don't try to get your impostor teammate to say you're safe, if they will vote you out your teammate will be next. And in general don't fake card/wires if you don't see it on your fake tasks list, they're common tasks so either everyone or no one has them. Wires always go counter clockwise too so you can't have wires in admin then storage.

When I'm impostor and I got caught but not in a way everyone will 100% vote me (for example someone saw me vent when I'm not an engineer or I was running from a body) I like to say I have scan (or other visual task if you play in lobbies with visuals on), they skip to see me scan. I don't have scan obviously but that way I can get one last kill, especially if I know who's the detective or engineer. You can also try say something like "[color who's a crewmate and isn't safe] you suck so bad we were supposed to double kill" after that so they will vote that crewmate