Repetition my friend. Mnemonics, cue cards, just rewriting notes. For example, when I did biology and had to remember the processes of something, I would write it down in note form with the help of a textbook, then cover it up and write what I could remember. Then I would re-write it with the textbook, and then cover it up again. I would do this over and over until eventually I didn't need the textbook to write it all out correctly. I would repeat this after 10 minutes, 20 minutes etc. until eventually I could remember it perfectly after a few days.