[Mithaldu]

Disclaimer: Not an artist myself, however i have learned much of the basics and am friends with many artists (e.g. http://kaceym.deviantart.com/ ) who earn their daily bread with commissions and have heard plenty about how they progressed.

The best way to develop them is, as with any physical skill: Basics, basics, basics. One doesn't become a master carpenter without hammering in thousands of nails.

This means, before telling you what to do, i need to warn you to not get too emotionally involved with any given piece. A day where you did 20 sketches in 5 hours will bring you forward. A day where you spent 10 hours on one piece holds you back. (At least at the start.) Don't bother with colors. Learn geometry, projection, proportions, lighting first. Colors only help to hide mistakes. Once you know all these things in and out, that's when it's time to start breaking rules.

Lastly, look up the books on drawing technique by Burne Hogarth and Andrew Loomis.