One of the ways I improved with character and creature designs was learning how real humans and animals are made up. Using references, I would recreate the images onto my sketchbook. When I came across a particularly difficult pose or figure, I would break down the shapes, sometimes by tracing over the image digitally, then trying again. It got me familar with a varitey of animals, body types, and the general flow of most figures. Most of these were independant studies, with a few done as assignments.
I would say the figure drawing has helped me improve the most, as it got me over my fear of drawing people. (hand studies were good for that too) They also helped me get more comfortable with creating detail by suggesting it rather than actually drawing it. For most of the human figures, their hands or feet aren't super detailed, but they aren't the main focus.
As you can see, many of the human sketches are posed like super heros, and that is because I grew up enjoying both marvel and DC content. My current favorite is Red Hood (DC)
In addition to the sketches, I often would add florishes around them, usually blocks or geometric shapes. It was the beginning stages of developing my eye for colors, which aids me in creating pallets and themes that work well together.