There is a "send figure to ground" option. It doesn't do so perfectly. Last step is to get in close, using an ortho view (side, front, etc.) and tweak the Y translate on the figure's hip until the feet are slightly inside the ground. A lot of people work from stock poses then tweak. Sometimes the tweaks are so much you can hardly tell what the original pose was. The biggest problem I have with stock poses is that many of them get to a position by using combinations of limb rotation and bending that are nothing like what a real human body would do to get there. I often find myself zeroing out lots of the channels and using a more appropriate bend to get there. After that, the art of posing is the same one any artist is familiar with; think about action line, balance, contraposto. Think through the gesture. Use a mirror and some props and see how your body solves the movement. That help?