For most men, the traditional grip is to use a single fist, held so that the palm of your hand faces you, sliding up and down the shaft of the penis. Since almost everyone discovers this one on their own, I'm not going to bother with any more detail here.

Pretty basic: as you're masturbating, push your penis down/forward so that it angles away from your stomach and more toward your thighs. It adds tension to the entire shaft and can either bring you to orgasm faster or make it more powerful.

My theory is that this feels good because you get the same thing from a lot of standard intercourse positions.