Well here is a basic tip that I follow:
Grab yourself some extra notebooks/exercise books and use 1 for each subject. At the end of a school day, come home and don't turn on the TV or try to steer away from any sort of entertainment. Now we will use maths for this short example. Think to yourself, "what are ten things I learnt today" or maybe "what are the things I learnt today" (you don't have to limit it of course) and write them down. Every day afterwards, try to do this while also attempting to recall what you had learnt the previous day. This for me refreshes my memory and helps me as I can recall notes far better.
Also, at the start of a new topic or a new chapter, read the syllabus and make sure that you understand what you should be able to do by the end of the topic. This will help for many subjects (perhaps not English) since you know that you have checked the absolute minimum requirements that any exam will expect you to understand.
A study timetable may help, for some it doesn't. I personally don't use one but it could help if you can follow it strictly :]
If you are studying for tests, I suggest finding some past papers and completing them and to read over your notes to see if you have remembered most of it.