Well first you can exercise the PC muscles. It's the equivalent of keigal exercises, but for men. Basically you flex and unflex the penis/taint muscles, strengthening them. The action is similar to stopping yourself while you're urinating. This will help you delay orgasm because when the muscle is strong enough, you can flex your PC muscle and hold off ejaculation.

Second you can practice ejaculation control. Masturbate until you're near climax and then stop. Let yourself calm down a little and then start masturbating again until you near climax and then stop again. Do this several times before allowing yourself to orgasm.

Give yourself some time for this to work and most importantly ... relax.