Focus on the build up and concentrate on her sensual spots before you go near her vagina to make her wet.
Most people seem to be referring to just the clitiros or inside, from experience (I have a mind blowing sex life) I say stimulate both, one at a time and together. Concentrate on her clit first, be gentle and make sure your finger is lubed (hopefully by her fluids), don't stimulate it directly at first (this can be just painful to some women when they aren't horny enough) maybe just stroke the hood until she is pretty turned on. You can then try stimulating her clit directly, again be gentle, try different patterns and pressures etc.
Once she is completely soaking, you can try entering her. Have your hand palm up and don't enter more than 3 odd inches, IME past this point there isn't much worth adressing. Find her g-spot and do the movements everyone talks about. Also move your finger in and out (still palm up) slowly wriggling the tip. This gets my GF moaning like mad.
Good luck. This should serve you well.