This is almost more of a trick than a technique, but it's effective and not always something that guys would think to do. Masturbate and bring yourself close to orgasm. Not so close that you accidentally go over the edge, but close enough that you're really, really excited. Then stop. Get up, put your clothes back on, and go about normal life for a while. Spend some time thinking about how horny you are. Or things that turn you on. And then after enough time has passed -- maybe half an hour, maybe a day or two -- masturbate to completion. I can guarantee you that the build-up will make for a better orgasm than normal.

You should also feel free to repeat the stimulation phase more than once before you finall come. If you get yourself fully erect and then let yourself return to normal five or six (or a dozen) times before you finally come, it's guaranteed to be amazing.