Here's a series of character sketches I created from abstract shapes. Here's how the exercise works.
First, Draw some random shapes on your page. Any shape, size etc. Now sit back. What do you see?
Let the shapes speak to you. It's a bit like making shapes out of clouds.
Now start drawing it in. Be flexible. Add lines and extra curves as you see fit.
You'll end up with character designs you never would have thought of otherwise. Now you can take them and flesh them out into full illustrations.