There are two positions I like for anal as well as vaginal entry. I like when she is on her tummy with her legs slightly parted. My legs go on the outside of hers. When entry is achieved I can nestle my balls between her parted legs and put gentle pressure and angles to good use. This is not so good for vaginal, nor is it a position you would want to pound her. Just a nice, slow sliding, deep penetration if she can raise her bum just slightly. A pillow can be put to good use, here.
My favorite, and one the ladies have really enjoyed over the years is with her on her side with her top leg bent up towards her breasts. (simms) I wiggle in behind her, my balls straddling her bottom leg. She is able to totally relax, and it allows me to get very good depth, and good control of the pressure on my balls. This is a good position for vaginal also, just a little different angles. It is not a great pounding position either, but nice for a nice, slow slider. A pillow can be used here also, and lets me get a little deeper. This is also an excellent position if she wants to hold a small enema while I slide into her. The enema can be given in this same position, and when she has taken all she wants, I can just get behind her and enter. I can massage her tummy and play with her boobs easily.
I sometimes get a funny look from a woman when I get her into this position for the first time. The funny thing is that on return visits, she automatically melts into this position as if to say " do that again, please". It is very relaxing for both parties. Quite often we will want to go crazy, and this position kinda falls apart as we get faster and harder, and will end with her on her back, or just a doggie style pounding.