I would say that for me, it's roughly 75% mental, 25% technique/stimulant. And by mental, I mean that I often need a big fat FANTASY (often involving other women) to get off... seriously.
And with the 25% technique part, I usually need to be hanging on to the bed frame and tightening my abs/Kegel muscles off and on, over and over again, to build up the tension I need to explode. This is almost all my part of it... as for my husband's part, the only thing I really need from him is to focus, very mindfully, on my clit and how it's linked to my brain (either that, or fucking me in the ass, which gets me off pretty well when combined with skilled clit stimulation).
When all of those things happen at the same time, I find myself ready for a mind-blowing orgasm. Needless to say, we don't often have the energy to get that far.
