Learn to be an Illustrator
Good drawing is the basis for illustration. Once you have mastered the fundamentals of drawing, adding color is not a difficult transition. The transition from line to tone is much harder, in my opinion, than the transition from tone to color. The reason for this is because, as a watercolorist I once knew explained, value is what makes a picture read. If you still have doubts consider this fact: Leonardo Da Vinci produced over 15,000 notebook pages littered with drawings in his lifetime, but left behind less than 20 paintings. He could paint well, because he could draw well. Likewise, Vincent Van Gogh insisted on focusing on drawing fundamentals for two years before he put oil to canvas. Mastery of the fundamentals is more important than any advanced technique. Included below are some suggested resources and reading to push you in the right direction. It will take years to master the above skills, but take heart - it takes every artist years to master drawing.
• Drawing Education