Drawing muscles like all others in our body operate at their peak efficency through regular activity or exercise. Betty Edwards' book Drawing on the Right Side of the Brain reminds us that 5 or 10 minutes of regular drawing exercise a day is collectively better than a hour of weekly instruction.
In leu of a figure drawing class, I find the best way to exercise that half of the brain is to keep a sketchpad and lots of pencils next to the couch. That way, I'm able to do quick gestures of the figures on TV, the easiest being cartoons. Powerpuff Girls and Dexter have some of the simplest forms to start with (the former having great villans).
The drawings are not designed to be displayed as finished art. These are just quick 5-10 second studies to help you see the shapes, expressions and movement of the characters - to take mental snapshots and quickly transfer this to paper. As you progress, you'll find it easier to capture quicker and more complex characters like Looney Toons. Of course genius and excellence in art will take more intensive hours of dedicated study and practice, but I believe these quick excercises will make that study flow easier and prevent "creative blockage". Now I just need motivation to get off the couch and exercise those other muscles.