I can help you out with that! I have gone ahead and collected over twenty tutorials to make your coloring even better. They are a mixed grab bag of coloring gems, sorted by the type of art supplies used. That should help you narrow down your range of options, or see what potential other media hold.
Master the art of burnishing. Use a very light or colorless blender or a paper stump tool to smooth out colors and minimize the appearance of pencil strokes. This will work better than your thumb, as well as giving you more control.