The better he can control his orgasm, the better your chances are for having more orgasms.
As you're stimulating him, get him to rate how turned on he's feeling on a scale from one to 10 (10 being the no-looking-back-now point). Drive him to distraction by revving him up to a seven or eight, then slowing it down again, several times over before letting him go all the way. Make frequent contact with his penis. If your hand, tongue or vagina touch it more frequently, it will be less sensitive to the touch and he'll last longer. If he starts to feel out of control, try giving him a squeeze. Squeezing the base of the penis firmly for a few seconds can delay ejaculation.
What type of orgasm are you aiming for?
If it's clitoral, choose a position where one of you can easily reach your clitoris to stimulate it with your fingers (or better yet, hold a small vibrator there). It's not cheating; it's simply acknowledging that's how our bodies work! If it's a front wall (G-spot) orgasm you want, try a a rear-entry sex position or a you-on-top sex position so his penis is angled the right way. Spread your vaginal lips once he's inside and press them against him to get maximum friction on your clitoris and the area surrounding the urethra. There's plenty of evidence to prove this area is also packed with nerve endings.
How he thrusts is also incredibly important: The traditional "jack hammer" style, deep, repetitive in-and-out thrusting, is about as effective as using a fork to spread butter. Instead, get him to grind his pelvis and move in circles, rather than up and down. The aim is to keep as much of the base of his penis in contact with the whole of the vulva as consistently as possible. Tell him to keep thrusting in short and shallow motions, rather than deep and fast
Use different stimulation for each orgasm.
You have a better chance of having more than one orgasm if it's via a different means. Alternate oral sex with intercourse with digital stimulation. (By "digital stimulation" I mean "finger stimulation," rather than digital as in television, but while we're on the topic, a bit of porn playing in the background could be just what you need!) If he's too close to orgasm, change the technique you're using. Get him to give you oral sex until he feels more in control.