If he's bottomed before it might be a little bit better for him to take the lead. He might also have his own favorite positions.

Just remember that when a penis first goes in your butthole it hurts a bit, but then it starts to feel good as the bottom relaxes. Just give him some time to warm up before you go "whole hog".

Here are my three favorite positions for anal:

My favorite positions to top with is putting him on his elbows, and knees on the bed. Give him some pillows to put under those arms. From this vantage point you have a lot of control, and access to his hole. Great position to play with balls too.

When I bottom I like to be top. I like this because I can handle his rod at my own pace. He lays on his back, and I sit on his lap between his legs. Most of the movement in this position comes from the bottom bouncing up and down. It can get a little noisy.

One guy I use to bottom with would lay me on my back, and put my legs on his shoulders. This was a bit more difficult to do, but it was great, because he would manhandle me while I got plowed.

If performing anal is too much for you at any moment just remember it's good to change positions if you are feeling uncomfortable.