Rangrz knows his shit right enough, and there are all kinds of techniques from tippy tongues horizontally on her clit quite fast to slow, vertical lapping at it it to big, fat tongued licks, to sucking and nibbling on her clit, all sorts. All women are different, what works for one doesn't necessarily work for another so trial and error it, see what works. You'll get some clues even if she's not the most responsive verbally reading her body and the size of her clit cos guess what: even women get hard-ons!

The most valuable line in the entire post though is this one:
ASK HER what feels good and what does not, or what she would like you to do.
If you're not able to read her responses it's for her to make those responses clearer for you, right down to
'do that some more, no, stop that, I don't like it.'
Can she orgasm by herself masturbating? You said
'she has told me herself she has never felt a climax' but I dunno if you mean just during sex with you. If she can then maybe she could masturbate for you and show you how she does it, what works for her. She might be shy about doing that, it might be a big turn on for you both, it will certainly be a big help though as far as giving you some clues goes.
Lastly, stop stressing about it. Anxiety during sex is guaranteed to be a problem, it would tend to move her further away from the very thing you're trying to achieve if the thing becomes a big pressure thing for her to come. RELAX! Take your time, explore each others bodies some more, experiment with each other, with toys, dressing up, creating an atmosphere, things like that. Sex should be fun, not something you stress over. Enjoy the damn thing whether she comes or not. That way you're more likely to get there in the end.