Whenever you draw, you will improve. You don't need a contest to improve. One thing you can do is post up a picture of a clothed model or something and have people draw that. You can draw it furry, anime, cartoon, or even realistically, whatever. Similar to life drawing, just with clothes so nobody can call it "suggestive". It doesn't need to be some sort of contest, though. Just keep it as a random drawing thing.

Random drawing things are good for practice. You will improve by participating in them. But art shouldn't be a competition... It's more fun to show off your version of the subject and see how everyone else did it. It will prove how different everyones artistic thoughts, styles, and the way people do things, are...