My advice would be to make sure you have plenty of foreplay to make sure you are really wet and "open" to be ready for penetration. He can eat you out, finger you - whatever. Just remain as relaxed as possible.
Then when it's time. Open your legs as wide as you can. This will help facilitate him being able to slip in. If you close your legs/tense up, it will be uncomfortable and it might hurt. Relax.
Keep your legs open when he's getting ready to enter you, as he enters, try to remain relaxed - breathe. It might be painful or not, but be relaxed. If you're relaxed, he'll be able to get in with no problem and start thrusting into you without issue.
Sometimes (from what I hear) the pain lasts a couple of days. Sometimes there is almost no pain at all. If you have a hymen to tear, and he successfully penetrates you, he may tear your hymen (pop your cherry) which can cause some bleeding. It's not supposed to be a big gush of blood but rather "spotting". If there is no hymen to tear, you won't bleed. Still may hurt a bit (depending on the size of his penis and how relaxed you are) but not bleed.