I mentioned the importance of paying attention to your testicles in Balls Just Want to Have Fun. But you can also stimulate your testicles hands-free, too. Start by sitting naked on something flat and soft, like a couch or bed (with your knees hanging over the edge) or padded office chair. Position yourself so that your testicles rest lightly on whatever you're sitting on. As you masturbate, sort of scoot/thrust back and forth. This should cause your testicles to brush back and forth against the bed, and also stimulate them further as they rub lightly against your thighs. I felt a little funny the first few times I tried this because I thought it must look silly, but when you're by yourself that really doesn't matter, and the additional sensation is more than worth it!