I try not to be aggressive unless I feel I really have learned a lot about the player. I've found it's best often to not buy the pot unless you actually know it can be bought; don't just through a bet out there hoping. You have to know it will be bought. If you get a call, then there's something wrong. Is it a draw or a slowplay? Knowing the player, you should be able to reason it out rather quickly and it's an easy fold or another aggressive bet.