Well, what works for me is I get down on all fours, then I put my knees on the edge of the bed, so he can just stand up behind me. Way easier for him!!! Then, like others have said, I rest my front end on my forarms. The further you bend your front section down, the easier it is for him to enter. And until you two get into the swing of it, you may need to reach under yourself and "help him" go in.
Also, for me, his legs are better outside mine. Why? Because sometimes, if his legs are on the inside, his thrusts and his legs will force my knees further and further apart and I keep sliding down, almost doing the splits, hehe. Its anoying!!!
Doggie style really is fun. You can kinda just rest on your arms and knees and enjoy!!!!
Ps---i like to wad up a pillow to lay my head on!