First off, stand in the shower and aim the showerhead at your balls, with the water as cold as you can stand. Try to endure it for a few minutes; you may notice your balls contracting into your body, but don't panic!
Now turn the temperature up, until the water is as hot as you can bear. (Be sensible about it-you don't want to spend the night in the Burn Unit.) Again try to hold out for a few minutes. Repeat the process, switching between cold and hot, around five-six times, or more if you like. When you're ready, masturbate using whatever method you wish.
When you orgasm, you should notice something very different. As your cum rises from your balls and passes through your penis, you should feel it as a very intense, hot surge, like very hot water through a pipe.
When I tried this, my penis felt very hot and tingly to the touch afterwards, and this lasted for several hours. The sensation was thoroughly arousing and I ended up wanking about eight more times that day!