This usually gives me orgasm in less than a minute! Start with your legs close together, but not quite closed, laying down. Start to tease your pussy, just brushing here and there, gradually working closer and closer to your clit. Then suddenly rub your clit very fast side to side, and after about 10 seconds slow down, but keep rubbing. Then go back to fast for as long as you want. Move up and down, repeating this cycle of fast and slow. As you get closer, open your legs very slowly as you rub. When you are on the edge, stop for a couple seconds, then go at it with all you have and spread your legs as wide as they'll go!
I also like to visualize this:
I'm on the beach. The sun is setting, and there's a huge wave out in the distance that is orgasm. As it's getting closer, it gets bigger and bigger, gathering speed. Just as it's about to hit me and the sun is about to disappear, there is a blinding ray of the last sunlight, that heats my pussy beyond imagination and gives me a huge burst of energy! Then the wave crashes and washes over me, giving me a huge dose of orgasm and pleasure!