For reference images there's nothing like a Google image search for "pose" to give you a bunch of images you can use to form the basis of your effort. So, I just did quite a few of them to get my head into the space.
Aside from the practice around getting your general angles and shapes heading in the right direction, it's actually also quite a bit of fun! It helps warm you up and to get your eyes looking at the important things first.
Some additional sheets:
Anyways, I really had fun doing these and did a few more on my flight back.