If you want to do an exercise for yourself, try to recreate or just be inspired by an existing work of art... Learn new techniques or something you hadn't thought of before... I've been working on and off on a particular Brom image that I really like. Multiple figures, interesting poses and use of light, custom textures AND transmaps for assorted clothing and there will be vast amounts of postwork and painting afterward. And it's not copyright violation... People go to art museums and paint pictures right in front of the real thing. It's an interesting concept called Learning. Just don't try to sell it and pass it off as your own :)