I participate in a wonderful initiative set up by Alyssa Nasser, called Ten Paces and Draw. Every week there's a theme. You make a sketch fitting that theme, send it in and you get someone else's sketch to finish into an illustration.
I got a sketch (on the left) and made it into the illustration on the right.
It's fun to do because I get the train my skills and thought process.
You can see my sketch here.
And my final illustration here.