I freaking LOVE flashcards, especially for my spanish class which has a lot of vocabulary. Not gonna lie, they're a pain in the butt. But they're insanely helpful for short, broken up study sessions. Here's four rules for flashcards.
Rule #1 - Cut your cards in half. Cards are expensive, especially when you're using 30-40 cards per chapter per class. Learn how to write small for goodness sake and get all the info you put on it.
Rule #2 - Be concise, make sure the information you're putting on your cards is as short as possible but still accurate.
Rule #3 - Give it some color, you don't have to color code your flashcards. But by writing them in a colored marker will just make them a little happier to look at. Assuming you're being concise (see Rule #2) you'll have plenty of room on the card to bump up the stroke on your pen. (design joke)
Rule #4 - Use the The Leitner System when studying flash cards. Basically how the system works is you have a few groups of cards. As you answer cards correctly, cards move forward, and as you answer wrong cards move back. After you go through a stack, you move on to the next one. Essentially, you're reviewing cards you know and not worrying about cards you don't as much. You'll get them eventually. Check out this handy graphic!