1. Make your notes as you go along, and take note of anything you don't understand when you're doing homework so that you can ask your teacher and understand before you have to revise for exams!
2. Keep simplistic notes... Limit your use of highlighter and try to keep to one colour of pen. Basically, you just want to make it as easy to read as possible.
3. If you're studying languages, try to listen to music in the language regularly as well as learning the vocab as you go along. There are complete vocab sets on memorise and Quizlet.
4. Don't be afraid to find a new way of understanding something... There was one physics topic that I just didn't understand until I read an A level explanation, and a biology topic that I found easier to learn through a podcast. Work out how you learn best, and utilise it.
5. Don't waste time... reading through notes passively and making revision posters often feels like hard work, but you take very little of the information in. You're also unlikely to look at the posters. It's better to spend 5 minutes writing down everything you remember about a sub topic, 30 mins using notes and textbooks to correct and add information to what you remembered, and another 5 minutes to see what you remember about the topic after revising it, than to spend 3 hours making a cool poster. Rest isn't a waste of time either, and it means that the revision you do will be of a higher quality.
6. You're cleverer than you think - it takes intelligence to plan ahead and to be willing to work hard. You'll be ok