This is a great start, have you done a back story on each one? As you design, focus as you have on different expressions, action poses and accessories. Practice drawing the basic shapes: Cones, Rectangles, Spheres and Cylinders. Then look a learning perspective, again a basic need to have skill. If you are looking to do digital drawing start with the simple 3d programs, learn and understand the principle of space and how your characters live in that space (again perspective is your friend). Keep going, you'll get there.