It is thought that masturbation before sexual activity will lessen the amount of desire a man feels thereby increasing control. This technique is not very effective, however, as level of arousal is only part of what contributes to the condition. Condoms are an effective means of reducing the amount of stimulation experienced during sex. Some men find that a condom helps them prevent premature ejaculation by lowering their arousal. If one condom does not decrease the stimulation enough, then put on one more.
Condoms provide excellent protection against STDs and pregnancy, so they're certainly worth a try.
Sexual positions can affect a man's ability to control his ejaculation. Try laying on your back, allowing the partner to control copulation. In this position you are more relaxed, and can guide your partner easily.