Easy answer: Laugh at him. You could also compare him to previous lovers, or get really pissed off at him. Best of all, try icy silence -- he should know what's wrong without being told, the selfish jerk.
Unfortunately, the reason those all work is that he'll never be able to get in bed with you again, so you'll have the opportunity to find someone better. If you're just looking to improve performance on your current model, though, you're going to have to try some other methods.
I'm not a sex coach, so if you're looking for specific tips or techniques, head over to The Big O. I'll tell you how to get him to try those methods without crushing his delicate male ego. Remember that he isn't bad on purpose, and he's not trying to be selfish -- he just needs a little help.
The trick here is to get him to try harder without hurting his feelings or letting him know that he currently sucks in the sack. To do that, all you have to do is keep in mind two basic elements of the male psyche: Ego and General Horndogginess.
Ego is important because guys always want to be the best, particularly in bed. The more you like it, the more he likes it. The more he likes it, the more likely he's going to do it that way again. That means that you should let him know when he's doing it the right way. Don't be shy. When you like something, say, "I like that," or scream, or otherwise let him know that's the right way. Conversely, don't do any of that when he's off the track. It's like that kids' game where you say "warmer" when someone's getting close to the prize you've hidden. For that matter, you might eve try saying "warmer" and "colder" to him. Whatever you do, positive reinforcement is the key here. (By the way, this principle works in reverse too: Watch his reactions closely to see how you're doing.)
Of course, depending on your level of comfort and the number of times you've done the deed, you can actually get specific with requests. But, don't be too bossy, especially the first time you're naked together (unless it's a dominatrix situation). Give him time to explore and get to know your body. If, after a few sweaty times together, he's just not hitting the spot, then try some more specific instructions. For example, tell him where to touch you, how fast, how slow, how hard -- you get the picture. Taking the guesswork out of those hard to reach places will speed things along.
General Horndogginess is even simpler: The better he's doing, the more you'll like it, and the more you'll want to do more of it. The better he gets, the more he gets. Even guys can understand a simple equation like this. While we're on the topic, remember that practice makes perfect: You'll both just have to reconcile yourselves to long, grueling hours of slaving away in bed. Sorry about that.