Anki!!! I LOVE that flashcard site and how you can set intervals to resee things that you find harder than others. On top of that, I also use a lot of mnemonics. Also, I got a small white board where I write things like organic chemistry reactions out over and over. Used in conjunction with Anki, I see a reaction and I draw out the reaction, then check to see if I got it right. If not, I make myself write it out 5 more times. Then, I bury the card for use again later in the session and do it again. I have to get it completely right twice before I'm done for the day, then I have to get it right the next day. If not, it's the same routine. This continues until the moment I know it cold. Soooo... basically what everyone else is saying - Anki, mnemonics, repetition.