Jared Wilson has a great post on...well the title gives you the answer. "Within the marital covenant, sexual intimacy can be a joyous, mutually satisfying, and mutually encouraging gift. But many husbands and wives don't know how to "get there." That is how it begins; you can read the rest for yourself.
It is not always an easy subject to talk about, but it doesn't have to be that way. In fact, it should not be that way. Like Z, I thought this portion of the article was most helpful:
Talk – Men are not wired very well for context clues, and because a woman's body has ebbs and flows to what she may find desirable, arousing, etc., men often feel lost. (e.g. That thing "worked" the last time, didn't it? Why isn't it working now?) Meanwhile his wife feels he doesn't know her at all. Look, men may not ask for directions, but they'll accept them if given lovingly. Most men really do want to please and satisfy their wives and find pleasure themselves in doing so. It is odd that many women will want to talk about everything on their mind but this one thing. It's okay to ask for something, to guide a man's hands, etc. And while, of course, it would be great if he just already knew exactly what you wanted/needed, nobody gets good at something without practice and direction. Given enough of that over time, a man of average intelligence and interest will learn how to satisfy his wife. Don't give up; give instructions.
Love in the Truth.