One of the most important and invaluable ways to practise for your exams is to use practice papers. This is a key exam revision technique, whether you are studying for your SATs, GCSEs, A-Levels or even your degree.
You can get hold of practice papers through the websites of qualification awarding bodies as well as (ahem!) via the First Tutors Resources section.
This is an important way to revise because passing exams is as much about practising your technique as it is about how much you know. You need to practise answering questions in the same time limit that you'll have on the day. If you don't you may well end up panicking in your exams, or devoting too much time to one question and not enough to the others.
Go through the exam paper first of all using your notes and books. This will help you to identify any gaps in your knowledge or understanding. It's vital you do this before you start testing your timing. If there are gaps, then take a day or two to reinforce your knowledge.
Then you can give yourself a test exam. Be really strict about giving yourself exam conditions. Time yourself properly and make sure you're somewhere quiet where you won't be disturbed (and where you can't cheat by looking anything up). Notice how you tackle essay questions and cope with the time restraints: make note of anything that worries you so that you can work on this before your real exam.