Maybe just look for picture of real people and use those as models. Find pictures of people walking or running or whatever, it shouldn't be hard to find some. Then base your pictures on that. I think it's much easier to have a model to look at than to try to think up or invent something from scratch, especially when you're dealing with something like the human figure. Unless you study anatomy, which many artists apparently do. Either way, you need to have an understanding of how the human body works in real life.