One thing which helps is doing several frames of animation. Once you start on those (e.g. run, jump, idle) you'll notice that certain things which seem optimal at a still frame are not when doing animation. I find that when doing animation I often have to change my initial design a bit (I mostly start with the idle frame), and make a few frames which only make sense/beauty in the context of the greater animation. It's easy to squeeze in a lot of pixel detail in the idle frame, but when doing a bit of rotation along various axises for the other frames the detail quickly becomes unwanted noise.