Invest in drawing books. Education is the key to understanding the techniques utilized in comic books. Though the focus will be to draw comic books, it's good to have a range of art books on different topics like vehicles, landscapes, and animals. Specialty comic guides include Will Eisner's Comics and Sequential Art, How to Draw Comics the Marvel Way, and the DC Comics Guide to Digitally Drawing Comics.
Focus on the basics. Though you may want to jump right in, there are some basic art fundamentals that need to be mastered first. Much time should be spent learning how to draw different spheres, cubes and cylinders as they will make up the basic building blocks of all drawings.
Sketch stick figures. Start with horizontal lines for positioning the top and bottom of the head and one for the feet. Estimate where the center point is around the groin area. Place a line there. Next estimate the center between the groin and feet. Draw a line and circles at each each end to represent the feet. Repeat for the rest of the body, focusing on chin, chest, and elbows.
Draw the stick figures in many different poses and positions like jumping, leaping, or flying. Repeat this until it becomes easy to draw them in any position you want.
Flesh out the different parts of the body based on the three shapes learned previously. Picture each body part as one of the shapes and use that as the starting point. Sketch it with that shape in mind. For example, arms and forearms are based on cones while the head is a sphere.
Vary the thickness of your lines using the thickest to outline the character. Learn about lighting, shading, and how to control your drawing hand. Don't be concerned about gray tones unless you don't plan on inking the character.