Basically, the Pen Tool is one of the most efficient ways to draw lines/outline things in GIMP and Photoshop. You click a point, and then another point, and it draws a line from point 1 to point 2. It's pretty neat. There are also other variations of the pen tool that can make curved lines, you can freestyle, etc.
But yeah, what Fenris said would be some better options than just trying to use a pencil tool, etc. Try experimenting with different brushes and tools. Example: I tend to use a low opacity smudge sometimes to make things look more blended, etc.
The more practice you have and the more experimenting you do, the better artist you will become.
Last edited by Faint; Oct 25, 2012 at 07:47 AM.