Foreplay : Sex is more than simply penetration. Foreplay can greatly increase the sexual experience in terms of both time and pleasure.
Behavioural Techniques : Try the ‘squeeze technique’ (squeeze the penis tip near climax to prevent ejaculation), and the stop-start technique (reduce simulation when nearing climax).More details can be found here.
Mental Distraction : An old classic. During sex focus on your attention on something deeply unerotic such as multiplication tables. This can reduce the enjoyment of the act itself but is often effective in delaying ejaculation.
Slow Down : Generally, the faster the man has sex, the quicker he ejaculates. Rapid, hard thrusts result in a faster climax. A slower, more measured technique means the penis tip is less stimulated and ejaculation delayed. It also allows for greater control over ejaculation.
Masturbate: Masturbation is perfectly healthy and natural. Masturbating regularly can help build up your stamina and thus enable you to last longer during sex. You can also practice behavioural techniques while masturbating so you are more comfortable using them during sex.
Condoms : Condoms decrease sensitivity and therefore usually increase the time taken to ejaculate. They also have the added bonus of preventing sexually transmitted disease and unwanted pregnancies.
Communication : Make sure you let your partner know what works for you and what doesn’t. An open attitude towards sex should also relax you more and lessen the nerves that cause a swift ejaculation.
Edited from Lloyd's Pharmacy