How do I vent
Don't vent. For the love of God, either don't vent, or only vent in order to kill. That's what you must do.
If you vent and others see you, it's game over… Unless you can kill them before they report you, of course. And hey, if you want to play some 4D chess, vent, and then accuse whomever saw you of venting.
But in general, venting seems to have more drawbacks than benefits, unless you're playing a game where the crewmates have incredibly low vision ranges.
Don't even pretend
I get it, if you aren't doing tasks it looks bad, but for the love of God don't pretend to do tasks. If you just stand next to a task doing nothing, and the task bar doesn't go up, you're the imposter, and it's clear.
Instead, you're much better off moving from room to room hurriedly, and the others will see you as a diligent worker, not questioning what you're doing. Then BAM, a knife in the back.
Sabotaging is great, of course, but you should really only do that when totally alone, it's too suspicious otherwise.
Find a friend and stick with them. This doesn't have to be a real life friend or anything, or even someone who likes you, just choose someone.
If you are sticking close to someone and not killing people, well, they won't suspect you, and will instead feel secure that you're nearby. If you pick a friend do not, and I repeat, do not actually kill them. Instead, while they perform tasks, dip out of the room, kill someone else, then return to your pal before you are seen.
Once the body is found, your friend will stick up for you unwittingly. "They were with me the whole time, it's not Blue" they'll cry, leading the others to their demise. This can also work if you're in a game with two imposters or more - just hang out with your own kind, stick up for one another. Unless you're being suspected, then throw them under the bus.
Well, we just made a friend, but these things don't last forever. It's time to betray them, brutally and mercilessly.
This is even better if you have a real life friend you're playing the game with. Help them as much as you can, stick by their side as long as you can, and they'll certainly assume it's one of the online randos that is the problem. Until they get a knife in their back.
Real life friendships are the easiest ones to abuse, and for good reason. I'm not saying you should end any friendships over this, but if you want to win, there's an easy way to the top. For a real life example, please look a global politics. It's called nepotism, either play the game or lose - and as an imposter, a true fake, you gotta play.