Sketches: Demogirl & Engineer
I thought I'd post up the sketchwork for the Demogirl picture, just for kicks. As you can tell, it went through quite a bit of polish between this state and the final art. Also included is a sketch of a female version of the Engineer class from the same game. Click to enlarge.

Comments
Wow! I like your sketching style. Are there any books or links on art instructions that you can recommend for studying?
Not really. I haven't read a single book on art in my life. I've just looked at other people's art and done what came to mind. Other than the classic advice of "divide your characters into basic geometric shpaes", there isn't much I could tell you.
Damn and I thought there was just some book that I would need to read which would magically make me improve on my art. So, do recommend 'copying'(well not 1:1 but rather trying to redo their pieces from scratch) other people's art for practice?
Absolutely. Art is 50% stealing and 50% practice.
I'll still say - the engineer is really kaawaaiiiiiiii ^__^ Keep it that way.