God made sex for only a husband and wife to regularly and passionately enjoy as an act of worship.
That is a good summary on the subject, but it's hardly exhaustive and it barely brushes the surface of all that could be said or discussed. There is so much more to say and talk about. So, let me encourage you to consider these Biblically grounded resources (click on any one of them and it will take you directly to that book on Amazon.com).
One final word before the list. Lots of people - especially men - will wince at the thought of reading a book about sex. "I think I know how it all works" is what many will think, if they don't come out and say it. The problem, though, is rarely with the raw mechanics. Those generally take care of themselves. Sex, as God intended it, is so much more than physiological. It's the culmination of mind and body and spirit. Don't fall into the trap that says you know all there is to know. Fellas - become the student again. Ask her to be your teacher. And yes, read some books. Here's the reading list (I own and have read all of these books):
God on Sex by Daniel Akin. This is a fantastic book that covers many aspects of sex from a pre-marital and post-marriage basis. Lots of cool questionnaires help partners objectively consider themselves and each other on a variety of issues. I highly recommend this book.
Sheet Music by Kevin Lehman. Dr. Lehman's style is easy to read and very straightforward. Helps with many aspects of the bedroom, but is pretty much for husbands and wives only.
A Celebration of Sex by Douglas Rosenau. Now we're into very specific technique issues, with drawings and illustrations. Explicit discussions about positions, orgasms, sensuous massage, sexual communication, mood, anatomy, etc, and Chapter 12 - "Creative Intercourse". Rosenau makes for a very good reference book, and the truth is that every couple runs into some of the issues and questions in this book sooner or later. But it's not the book you want your 8 year old flipping through. So keep it in the drawer when you're not reading it.
Sex Begins in the Kitchen by Kevin Lehman. I think Dr. Lehman is one of the best writers of our day on marriage and family subjects. This is an excellent book that will help any couple who's love life has become stale to put some spark back in a healthy, mutually satisfying way.
For Men Only and For Women Only by Shaunti and Jeff Feldhahn. These books are not only about sex and intimacy, but if you don't understand and practice the principals in these 2 small books (one for men and one for women), you will likely always have trouble with intimacy, in addition to other areas. I highly recommend these books.
Finally, The Gift of Sex by Clifford and Joyce Penner. This book is down to earth, pretty explicit but extremely practical.