I like to cinch up my balls to enhance masturbation. I take an old knee high or an old stocking, wrap it around the base of my scrotum (including my penis) and then tighten it up as far as it will go. Then I like to tie it in as many knots as I can, as many different ways as I can, to make it as difficult as possible to untie it. With the stocking cutting off the circulation everything starts to turn purple and the head of my penis looks and feels like it's going to burst. The sensation is incredible, everything gets super-sensitive. A few times I've tied it too well, and I had to run to grab a pair a scissors to cut the nylon.

One variation I also do is to tie the stocking just around my testicles, leaving my penis free. Masturbating like that really heightens the sensation too.