Make friends with the stick figure and Cylinder Man. I picked that tip up from Learn How to Draw Comics The Marvel Way and an artist named Scott McDaniel. Learning to draw quick stick figures with proper proportion is a great confidence builder and a fantastic warm up! Do them by the dozen when you start drawing everyday.
Cylinder Man is a beefed up version of the stick figure. After the stick, draw cylinders around them, joint to joint, to match areas of the body. This will help you draw muscle groups and begin your journey into foreshortening. It also forces you to build your figures from the inside out. Your drawings aren't outlines of shapes, they are layers and layers of line to create shape.
Keep it loose and sloppy. Make mistakes. Stop using your eraser and start over. Learn to draw from your elbow, not just your wrist. Every now and then, look at what you've done and say, "Damn! I'm good!"