The first thing you need to learn to know about the heads-up situation is is to keep at your guard and maintain the care, discipline and attention that brought you to the last stage of the heads-up tournament. After playing many games, both you and your opponent must be tired, and you can take advantage of his fatigue and maybe cause him to make a few mistakes.
The heads-up part of the tournament is also the most stressful part, because after coming so far you don't want to fail with just one other player left in the tournament especially when there is so much at stake. Play your normal game, and if you need to, take a break and relax a little.
If your opponent is better than you, the right strategy to use during the heads-up stage is to play aggressively. This means you should try and clean out your opponent and knock out out, usually with a a high ranked hand. If you manage to win a huge pot but he still stays in that could still be good as it may cause his morale to drop.
If you are a better player than your opponent, you should play your usual poker game and avoid taking such risks.
The most important rule for playing heads-up tournaments is not to play the game too tight. This is because if you play it too tight, you will lose accumulating antes and blinds. In this instance you are allowing your opponent to gain easy chips without doing anything.