Minecraft – How to pose the Minecraft Player

Your best bet for an in-game solution is Smart Moving, which adds a tonne of new animations to the player. While you still can't make a static 'pose', you will have a vastly greater range of motions:

Feature: Head Jumping

This mod implements the possibility to jump head first instead of head up.

To head jump start sprinting and press the grab and the jump button. When the jump button is released you will jump, head first, with a angle depending on how long you pressed the jump button.

Hitting ground while falling with your head first will damage you more than hitting ground with your feet first.

Feature: Side & Back Jumps

This mod implements the possibility to jump to the side or back while straightend on ground.

To jump left double click the left button, to jump right double click the right button and to jump back double click the back button.

You can also jump back-left and back-right by double clicking both relevant buttons at once.

Feature: Climb Jumps

This mod implements the possibility to jump up and back while free climbing.

To jump up climb up as far as possible and click the jump button.

To jump back stop climbing by releasing the forward button press the sneak button to hold the height and click the jump button.

You can also head jump back instead by releasing the grab button after pressing the sneak button and before clicking the jump button.