I just recently returned from a successful tour deflowering a female. Here are my findings:
1. Get her wet, turned on and reassured. If she's nervous/afraid it will NOT go in or will be very hard to get in.
2. Stretch her out first (may take a few weeks/months if she's really tight) with either fingers or a vibe/dildo or both. I think two fingers is usually enough...Three is a bit iffy, touch and go etc.
3. Probably lots of foreplay, make her cum a few times. I didn't really have to do much of that though...
4. The Secret Technique: Hold your penis at the base, half way up so only half of it, or a small part of it will be going inside her...say 4-5". This way, you can keep your hand there, stopping full penetration which could be painful. And, when she's ready you can do her hard. Eventually, you can move your hand further down to allow more in and maybe even not have to use your hand at all.
Good luck.