For now you should play non-antag roles, learn as much as you can and observe some rounds to learn antag tactics.
Since people do not mind super knowledgeable antags it's your best bet.
And then you gotta find antag role specific tips, like how to use your vampire abilities [and not get lynched] or how to prepare yourself as a nukie [and not get lost in space].
basically the more you play the game and the more antags you fight, the more robust you become. You start seeing useful things (hide in that locker NAO!) and knowing where everything is.
I don't play antags myself (just aliens and very rarely vampires), but this is what I could gather from seeing good players in action. Knowledge, tactics, luck.