You always need to identify your opponents.
Postflop:
If they are overfolding, bluff with any 2 cards at least once (don't have to bet big)
If they are overcalling, medium value hands become nuts.
This has everything to do with both of your ranges and how both of you would play those ranges.
Preflop: depends on the stage of a tournament, stack sizes distribution, bubble factor, estimated fold equity against a particular opponent (depends on your relative position at the table), even your own image.
But try not to overthink, don't level yourself into
a 4bet-bluff push just because of vilian was 3betting lightly lately. He might bluff 3bet you, but when facing a 4bet-push for 30 Big blinds, he won't be able to fold just because. Yet again, know your opponent.
It just takes time, it's a game of skill after all.