How can I make sure sex doesn't hurt?

I agree with everyone so far. Basically, make sure you've had enough foreplay and that you're not only wet enough, but that your labia are fully engorged. Most guys mistake a girl being wet as the sign to go, and they finish up before she's about to go to heaven. Make sure he is patient. Also, as most have said so far, don't worry about what you're doing too much. If you worry, your PC muscles (the muscles at the entrance of the vagina) will clamp tight, and if he forces it further, it will hurt more. Also, make sure that you have lube with you. Virgins often tend to not produce as much natural lubrication as what girls that have more experience do.

New thing to add: I think Kayen-of-Umbra came close to saying this, but here it is anyway. A doctor can perform a minor procedure called a hymenectomy. Basically, he will surgically break your hymen for you. That takes the fear that your guy will hurt you when he does it away. That should help you to relax just that much more.

Make sure he wears a condom, and try getting onto the pill long before you have sex the first time. They're not perfect, but they will help prevent pregnancy or most STI's.

I'm going to agree with jessica and add one more thing theirs I don't know what their called but doctors say to use them if you are "small". Their like similar to dildos but their use more for stretching the hymen

And if you do certain rigorous activities they can also help with breaking the hymen before sex

Try lubrication, and lots of foreplay, for example, oral and fingering, make sure you are not tense. But as others have said, make sure you feel it is right before you make your decision

Use lubricant. You may try a small vibrator to get your body used to penetration. But I would recommend not having sex until you are in Love and in a serious relationship. There will be other boys.

So are you a virgin?

Well don't seem to nervous. IF YOUR READY that is don't rush

And it sounds wrong but stretch it out

Finger yourself a lot. Make sure he fingers you and gets you very wet. Use lube also. And a condom of course. That not only will prevent pregnancy and STDs, but it will make it hurt less. Make sure you are comfortable and relaxed. If you are worried or feel uptight or tense, don't do it. Wait for another time. :) Make sure you really like him and he really likes you. Don't do it because your friends are.