There are 2 types of masturbation techniques physical (your hands only) or Mechanical (use of vibrators sponges etc.) I think most people employee the mechanical method in an attempt to enhance the pleasure and to prolong the euphoric sensation as you orgasm.
A method that I have developed over the years and believe me I have tried all kinds of methods,is safe, simple and will greatly enhance your orgasm experience.
When I have lots of time I will use an Excercel cockring.(other rings will do but I find this is the best one).This ring is made of an adjustable rubber with a relief that does not crimp off the uretha but allows the cum to flow. I tie a length of 1/2 to 3/4 elastic material,(similar to underwear waistband) available at most fabric stores, marts etc.) The other end I loop under my balls and loop through the other side of the cockring before pushing onto my Penis. Once you push the ring down to the base. Gently pull the elastic tighter to pull the ring towards your penis base and put some pressure under your scrotum. This will cause your balls to extend and move forward a little. You don't want to pull the elastic so tight that you loose the elasticity so your balls can't move but tight enough to provide additional friction to the underside of your bag and balls. I usually loop the loose end of the band back under my scrotum and tie it off on the other side of the cockring. Make sure the elastic is not twisted but lays flat under your bag. Someday I'm going to get some velcro sewn on or add some snaps to make the setup a little simpler. Using lube on the cockring goes without saying.
I find this arrangement helps to delay orgasm. It is possible to feel muscle contractions as you masterbate and not actually cum. If you use the edge technique and bring your self to the brink and back off. I typically lay on my back and read porn or watch a porno video as I rub on the glans and underside of my penis.
When you do decide to orgasm raise your legs up about 6 inches, the combination of friction behind your bag and the cockring not impeding the cum you will have a memorable orgasm and shoot cum a couple of feet. The key here is to take your time, don't get the elastic too tight.