I think what makes a good lover is one that not only knows how to seduce the body but also the mind. If you can take a woman away to a "mind fuck" fantasy... she'll cum.
It can be pretty common, when you are with her communicate with her to find out what feels good when you go own on her etc so you learn what she likes specifically you may also want to introduce toys ... learn about where her g spot is.
If they have NEVER climaxed, then chances are there is a psychological reason...I haven't ever been with one that didn't, but have had some that took more work to get to that first one then others, but after that it usually levels out. It is important for whoever the chick is with to make sure she relaxes as much as possible, NO ONE likes to think its obligatory, and if she's feeling AT ALL pressured, then the dude is sooooo fucking it up...