I'll speak for myself as an artist: sometimes it's really difficult to look at a blank piece of paper and invent something. I need something to spark an idea.
If you've ever looked up at the sky and saw random cloud shapes that looked like a bear, or a dragon, or whatever, then you understand what it's like to invent and imagine. Well, there is a new program called Alchemy that helps artists design and invent by generating random shapes. After doodling in the program for a bit and creating some random shapes using the mirror tool, I imagined seeing a greedy goblin character. So, I sketched it out based on the shapes, but turned the shapes into the character above.
To download the free program, go here: http://al.chemy.org/
Check out some of these YouTube videos for tips and ideas. They are really inspiring!!