Another technique is to place just the index finger and thumb around the penis about halfway along the penis and move the skin up and down. A variation on this is to place the fingers and thumb on the penis as if playing a flute, and then shuttle them back and forth. Another common technique is to lie face down on a comfortable surface such as a mattress or pillow and rub the penis against it until orgasm is achieved. This technique may include the use of a simulacrum, or artificial vagina.

http://en.wikipedia.org/wiki/Mastubate