Ok, so you have made the money. Now what do you do? There are several things to consider when entering the heads up stage of a sit and go tournament. On one hand, you are just not going to go too wrong at this stage by being aggressive; however sometimes being over aggressive is not the right strategy either. A lot depends upon the make up of your opponent when heads up, but as usual, blinds and stacks are the biggest factors in your strategy.
I think it is critically important here to realize the value of your hole cards because at the lower levels, that skill alone will win you tournaments. You will be surprised at how many of your opponents will be playing J5os and 73os and the like. Now it's not wrong to play any hand heads up, but to go all in with that crap preflop is definitely negative expected value (-EV).
It is not really skill as much as it is getting a handle on your emotions, impatience, and the Sklansky hand groupings. Your opponent's duty is to raise, so do not take it personally. Try to let your understanding of the game channel your actions, rather than your anger. A lot of times, you are simply going to either get outplayed or outdrawn. If however, you are in with the right situation, and ahead you have nothing to be angry about. You made the right mathematical move. That strategy will pay off long term. It does not really matter what happens any one given time.
Keep in mind that your stack size in comparison to your opponent's is what will be driving your heads up strategy. Whether you are the leader or trailing you have different considerations and the value of your hand is relative to your stack in a preflop situation.
In other words, there is so much opportunity to take a pot without going to the river that your position and stack are as much value as your hand itself. This is true for being both the short and big stack in a heads up match because a mistake here will have drastic swing possibilities in the match. For preflop moves though without cards, you really have to have a good read on your competition.
If you have not got holdem indicator yet, the Sklansky [http://www.pokerbookreport.com/davidsklansky.htm] Group ratings are just another reason I think it's the best poker calculator on the market. I use it during all of the sit and go matches I play.