What can I do in bed to make him happy?

Well, you can show lots of enthusiasm! Also, be the aggressor and just start having your way with him without asking his permission and without warning him first. He could be really turned on by that. ;-)

Just jump him when he least expects it. And remember, it does /not/ have to be confined to the bedroom only. There is plenty of other spaces, such as shower, kitchen, living room, car, elevators, parks, boats, airplanes, hotels, motels, castles, libraries, and so on.

Variety is the spice of life and just make sure that you are also totally into it as well.

1) whenever he is horny go for it right away 2) try some new positions and such 3) do it multiple times

Well try something spontaneous.Usually no matter what a girl does,a guy in the spur of the moment will get turned on by anything.Dress up in a little kinky outfit that he would like,or suggest new things that could be done.Personally,I think anything other than normal would make a guy happy.

If you wanted to surprise him with it,then wear some lingerie and just make a move on him out of nowhere. Just make sure it's not at a bad time.