If you are reading this, I presume you have some talent for sketching and drawing. In any case even if you aren't exactly Van Gogh, you can still learn to draw comic book characters. Once you have the practice and skills, it becomes fairly easy.
Before you begin drawing characters it is very important that you go through as many comics as possible. This is essential as it helps you understand the various drawing styles and techniques. Part of the process of trying to perfect any talent is to practice as much as possible. Keep sketching and try out different styles but along with this, it is equally important to discover and introduce your signature style. Try not to imitate. It will also help if you can take drawing lessons from a trained professional. Even if you are pretty skilled at sketching, you must go back to the basics, because drawing landscapes and human forms is very different. Human figures are not necessarily everyone's cup of tea.
There are mainly two techniques you can use to draw comic book characters. One is where the image is drawn using blocks, much like the human wooden mannequin, which is used to teach students of art, the other method is the use of long strokes to create the basic profile of the figure. The basics of line art drawing for any raw sketch is drawing dark straight lines to mark the major bones in the body. While drawing these characters, one must remember that these figures are highly exaggerated as compared to other types of sketches of human forms.
To draw these characters in action, for example punching, crouching, and jumping, keep in mind that the muscles alone can't help you create the movement. The bone structure must be exaggerated so that the muscles appear sturdy. Keep track of minor elements like the limbs, expressions, etc., especially when drawing female characters. For instance, the nails of male characters are drawn square and the nails of female characters are drawn oval.
To make the movements more prominent, remember that other facts come into play, for example, to show a kick you have to make the air seem as if it got lifted and don't actually show the impact. The reader should only see the aftereffect of the kick and not the kick actually happening. What I'm trying to say is that if the character is kicking the ball then his leg must appear as if he is bringing the leg back after the kick and the ball should be just gaining height in air.
Once you have perfected the art, you can work on developing a strategy which makes you tell the villains apart from the good guys by their costumes. That means the mean guys should have such costumes, that by just looking at the figure you now he is bad. Usually the good guys are more charming and good looking, whereas the bad ones are more rugged and mean in appearance. Now that you have the basics under control, do enough research so that you can draw characters with ease and finesse.