In year 10, listen in class, do your homework, and ask about anything you don't understand - especially in maths, never go into the next lesson not understanding what happened in the last one. So many people in our maths lessons would say "she goes too fast!" or "she doesn't explain it properly!" The problem being that they never actually told the teacher this, so how was she supposed to know? So whenever you don't understand, ask until you do understand.
Other than that, don't worry. There is only so much you can do in year 10. You will forget most of what you learnt in year 10 by the end of year 11 and have to revise it all again - that's perfectly normal. As long as you understand it at the time, that's the important thing.
Also trust your learning style. At exam times people will equate the quality of your revision with how many notes you've written or how many hours you've spent revising but that's just not true. You have to revise the right way and at the right time for you. I'm a crammer - I can't revise properly until the day before the exam. Then I spend the whole day literally cramming everything. I got 10 A*s. I tried to be that person who makes neat notes for weeks before the exam and revises in moderate chunks but I would just forget it all again anyway. So do revise, but figure out what way works for you and do it in the way that feels right for you.
Finally don't get disheartened if you get bad marks. You're still learning. If you get a C, don't see it as that you haven't got an A/B, see it as that you haven't got an A/B yet. Ask the teacher what you would need to do to improve and try to do that. Ignore your predicted grades - just keep trying to do a little better each time and see how far you can go.
Finally - enjoy your summer!