I've been drawing character sketches for my RPG characters for about 20 years. I've uploaded a few so some online friends can see my meager efforts.
My style - if I can claim to have one - is based on observing how John Bryne and Jim Lee comic art looked, and trying to emulate their techniques. I do an original in pencil, photocopy it, then use colored pencils to produce the finished work. Most of my stuff takes about 2-4 hours. Though particularly detailed stuff, like the few with backgrounds, took more like 6-8 hours.