Pumblechook
Just Browsing
lube, foreplay
lol, although concise, I believe I agree with the above age-old addage. I've had a gf before who was a virgin (also petite, not that it factors in). She was very wet and had no trouble, barring the very first time and in general, getting the head in (the hardest part). Once that is accomplished it is smooth sliding. I also never have sex without a lot of warm up/foreplay, which leads to relaxation and wetness. And of course, if there is no natural wetness, lubrication works too.
Perhaps building up steam as far as pumping goes will help you guys also. Don't just go slamming about right off the bat. You can feel when you are comfortably in and able to move about without resistance. I usually start with a slower pace and eventually build up over the course of sex. Not neccessarily a straight upward sloping line, but in general over the entire course, the pace quickens.