It depends on the guy.I'd say the first time you're more nervous,a bit scared,and not relaxed.Personally,my heart rate was through the roof and hormones were out of control,but I handled it fairly easy.
Your right you don't know. Try and go really slow and spend a lot of time on kissing and foreplay because sex is learned and your not going to be the greatest lover the first time. Everybody likes different things so ask her what she would like and after you have done it cuddle up with her and make her feel wanted and loved. That's the best way to get more experience.
