Definitely lube and go slow - she's probably heard horror stories, so she's going to be nervous. Lots of foreplay. And then, if it's excruciatingly painful for her, stop. There may be a medical reason for the pain (I've never had sex that wasn't excruciatingly painful - it's AWFUL), so don't pressure her. My guess would be that even if it did hurt and you had to stop, she'll be more willing to try again later to see if it'll be better the next time. Just don't make her feel like she owes you sex - that would end badly.
use some lube; or even ur spit and finger her first start with one finger work ur way up then use two;
next insert Ur penis but gently don't thrust it . its going to hurt her either way but do it slow and talk to her let her know its gonna be okay and that you love her; only say that if you really do though of course but talk to her; the first time may not be the most existing for her because its gonna hurt but after that she will love it!
and make the surroundings nice like candles that would be great!