Theres a list of things.
1) kegel and while doing so, breathe deep and mentally visualise drawing the energy away from the genital area.
2) Doing maths excercises, such as the times table, to keep your PC muscle relaxed.
3) breathing deep and keeping strokes at the base of the penis and light.
4) let go of the penis (and do any of the above).
Hope this helps.
You can also read this:
Man Health and Multiple Orgasm