Teachers are especially helpful when you have problems understanding aspects of subject content - but they may also be able to help with revision techniques.  They could help you to work out a revision timetable.  Ask them about (after-school) revision clubs.

Although they may not always be able to help with subject content they can be useful.  They can make sure that you have a quiet space to work in and that you are not being interrupted by younger (or older) brothers and sisters.  They might help out by buying you appropriate revision aids (folders, etc.). Some parents offer cash incentives for achieving a specific number of passes - or particular grades. You may be able to persuade them to be a bit more creative with their incentive schemes, depending on what you think would help you.

Older brothers and sisters can be especially helpful if they have recently taken exams in the same subjects as you.  Even if they took different subjects, they could still help you to understand your revision notes.

Get together to study.  One of the most effective ways to learn something is to teach it to others.  Form study-groups.  Talk about what you have learned recently.  Phone your friends when you get stuck (but don't just spend the evening chatting.  Text them.  Test each other frequently.

There may be those with whom you are not particularly close friends but who may be able to help - find out who's good at what and get them to explain any difficulties you may have.  "Geeks have their uses."

Explore your local library for useful books. Keep an eye on the listings for useful TV programmes that may help to enlighten your subject. Radio programmes can be just as useful as TV - as can video. Keep an eye open for useful computer-based revision programmes.

There are loads of useful sites. Some will focus on revision skills (like this site) - others will be subject specific. Remember to mark your favourites - and e-mail them to your friends.