A method that I've been toying with: dissect the proof into multiple simpler proofs, then dissect those even further if necessary. For instance, if you're proving that all X are Y, and the proof proceeds by proving that all X are Z and all Z are Y, then make 3 cards: * One for proving that all X are Z. * One for proving that all Z are Y. * One for proving that all X are Y, which has as its answer simply "We know all X are Z, and we know all Z are Y."

That said, you should of course be completely certain that memorizing proofs is worthwhile. Rule of thumb: if there's anything you could do that would have a higher ratio of awesome to cost than X, don't do X before you've done that.