Leri Greer was a graphic designer before joining Weta as a Concept Designer/3d Modeler, and was able to use his early graphic design experience heavily for DISTRICT 9. His most recent work includes similar duties on AVATAR, as well as being the creative vision behind the 2009 PC game NEOTOKYO. If you enjoy looking at drawings, his site http://pushbak.org has over 500+ sketches available to click through.
His advice for anyone wanting to work in concept design, or design in general, is just to be drawing, painting, and designing all the time, and to build your portfolio to a point where a company would be stupid not to hire you. If you ever see amazingly deep portfolios, with tons of work, and wondered how it's possible for a person to have produced so many drawings and paintings, it's probably because we work 10 hour days of nonstop art creation. In one month that's 200 hours of drawing, painting, and designing.
Even a monkey handed a wacom tablet and stylus would probably have a pretty good portfolio after a year clocking in close to 2,400hrs.