I don't know if this has been mentioned as a technique, it is a pretty long thread, but this has worked on my previous 2 partners.
Usually we start with normal foreplay, I've not noticed a major difference if she cums clitorally beforehand or not but I know she certainly enjoys. anyway...
- she lays on her front enabling her to relax but at the same time meaning I can assert some control if needed ie. pushing her into the bed or pulling her hair a little.
- From behind i insert my thumb into her vagina meaning I can put pressure directly on her g-spot
- this also allows the index finger to stimulate clitorally.
- the motion to move is actually up and don, perpendicular to the ground instead of in and out. Usually it's easy to see how fast to go but a nice slow build up to actually being quite forceful and rough seems to work quite well.
I've manged to make her squirt several times in one session this way!