I was playing a STT last night and I found that I don't really know how to play heads up when you have a marginal chip lead or when your chip stacks are very similar.

I can do it when I have a huge chip lead, All-in, All-in, All-in. and I'm not bad at picking my spots when I am short but as soon as we have similar stack sizes I seem to either play too many hands and get caught too often or don't play enough and get blinded down.

What sort of hands should you be playing in this situation of a heads up and what sort of raises should be made to apply maximum pressure?