Hmmm...
Well, firstly, I agree with Riva, as Gimp is my personal favorite when it comes to image editing programs. Photoshop also works.
When it comes to art (especially if you're serious about it), I'd recommend getting an art tablet, that way you can draw digitally with your pen and tablet.
However, if you're like me, and left with your program and just a laptop touchpad/computer mouse to draw with, I'd suggest that you try this strategy:
1.) Draw an outline for what character/art you'd like with pencil and paper.
2.) When you're done, scan it into your computer.
3.) Make a second copy of the file, and edit it to your delight.
- The pencil image will have very fuzzy edges, but at first, just color in the main parts
- Then you can can darken the inside colors, and go over the outline you drew with the darker shades.
Experiment with this, if you'd like. c: It's the strategy I use for my digital art (like my siggy), and while it's really quite time-consuming, using an outline you drew previously can be a life-saver.
(If you can get an art tablet, though. Do it. XD)