Gather all your material for the topic area and reduce them into brief, clear notes. Then summarize those, and then again and again until you only need a few keywords to remind you of the whole topic! (The S-cool! summary revision notes are a good place to start). You can then carry around a sheet with all the keywords wherever you go.
An effective way to make sure you remember certain things is to invent mnemonics. For example, Peter Went For His Early Morning Jog or MR E RING.