In the early stages i think you should play very tight, especially from early position. You can afford to play a wider range of hands from MP and then your widest from late position. Feel free to see cheap flops with suited marginal hands from late position and the blinds as long as you have the right pot odds
In the middle stages (60-120), you should still play tight from EP and MP, but you should start stealing the blinds from late position. Be prepared to shove on the button with a short stack, if you have to.
If you make it to the bubble, your #1 objective is to build as big of a stack as possible, to make it to first place. You should be playing aggressively, by stealing the blinds and forcing your opponents to make decisions.
In the final table, you should start playing very tightly again from EP and MP, while still being aggressive from LP. You can no longer afford to see cheap flops. As the final table gets short-handed, you should play aggressively from all positions.
Heads-up is when you should play most aggressive, forcing your opponent to make a decision. I recommend you study and practice your heads-up play.