Just make sure you're checking those answers too! If you see an area you get stuck on, then go back through your notes and relearn the content; do those excersises from your textbook. Because there's no point in past papers if you don't know the content of the exam inside out. And if you're constantly getting stuck on the same areas, then you know it's the ones you need most practise with.
Practise papers are really the only way to do it though - learning what the examiners want (by marking your own work with official mark schemes) will allow you to pick up extra marks in the real thing. Getting used to the style of questions, means you won't go into the exam completely unprepared.