This was from a WSOP
FT live stream discussion: You can't win pots when you fold. Another nugget was: if you're not sure what to do in a hand, aggression often is the best option.
I'm not advocating going out there and getting all reckless trying to run over the table, it takes experience and study to know when to apply pressure and when not to. If you're going to make the choice of whether to be aggressive or be passive though, being aggressive is the much better option in general.
TAG-style poker is the best place to start, but if you're moving up to where you're playing against good players who are watching what you are doing (especially over the course of multiple sessions) you have to vary what you are doing. Otherwise, you will start to notice that your opponents always seem to fold when you have the nuts, and drop the hammer on you when you don't.