Observe 1 or 2 hands, if they play really tight, i mean, if almost all players have folded, you can play aggressively on them, betting and 3 betting (cause some players will also think that it's time to steal pots), but if you get reraised, or 4bet, just forget cause you'll probably get caught dominated. But if there are several players playing the hands and trying to win the pots, just fold most hands cause it's not worth the risk. Besides that, all you have to know to have a basis on what to do is to observe your opponents and categorize them.