If you're talking about tournaments, it depends on where you are in the tourney.
At the beginning, don't go 'all-in'. I've found that the beginnings of tournaments, especially at the lower level are 'all-in' fests, and you could put yourself out very early, because someone will get lucky.
As the tournament continues, you need to take notes of the other players, and their style of play.
Are you in against someone who plays many
hands, or few hands; never folds, frequently folds; continually raises, or continually calls.
You have to make a judgement, just not on the cards you have, but on the habits of your opponents.
So, as the tournament goes on....watch, and act carefully.