Take notes whenever possible and check with friends.
Make sure, that when you are in class, all your notes, books etc are clean and that you have them! Also, pencils and glasses :P
Don't be afraid to ask the teacher for help.
Exams
Have a light snack when doing the actual exam...
Before the exam, don't take on too many things. Your mind should be relaxed and focus.
Homework
Take regular breaks
Say to yourself 'If I complete my homework within 50mins, then I'll watch t.v'
Always work at a desk and make sure your chair is level with the desk so you don't end up kneeling on your chair or slumping ;)
Keep all distractions, such as t.v, radio or another sibling away from you! Best work in silence.
Have a break when you come home from school, but not too long!
A homework timetable is great especially if you have a problem with time management, or have little time :)
Never attempt to do your homework on the bus/coach �V you may miss your stop, you could lose things, it's not good on your back and your writing would be messy. Plus lots of other things ;)