Irene Gallo, the spectacular art director for Tor Books (she's delivered three knockout covers for my three novels) has a blog, and she's inaugurated it with a long post of great advice for prospective cover-artists:
SHOW THE CLIENT WHAT THEY WANT TO SEE
Know who you are showing your work to. Don't show your still-lifes and say, "But what I REALLY want to do is fantasy book covers." If that's what you really want to do, then sit down and create a new portfolio. And don't offer to do a job on spec to prove that you can switch gears.Create different portfolios for different clients. The presentation you show a card gaming company may be subtlety different than the presentation you show a book publisher.
CONSISTENCY
The "Weakest Link" principle reigns supreme. Especially when looking at portfolios from young artists just out of school a couple of years. I need to know that you are in complete command of your craft. If you have seven paintings that you really like and three that you're not fond of, sit down and paint three more pictures. An AD will always fear that they could get you on a bad day. ADs don't want to take a chance on new talent, they want to feel comfortable and excited about working with new talent.
(via Making Light)
