Get some Bob Bly books, too...
Bly's a good ref. to have. He spends more time on the nuts and bolts-- types of mailers, clients, marketing tactics, measuring response, etc. I'm new to the game, too, and those books are great. Also, I have learned a tremendous amount (for free) from
www.copywritersboard.com.
And be sure you allow a lot of time for this to happen, depending on your life situation. Bowerman did this in a few months from scratch, but he has a background in sales/mkting, no kids and quit his job to jump in full-time. I have two kids, teach college writing courses (thus, lots of outside grading), and no background in sales-- mine is in writing. So it's taking a while to get it all going. But practice, practice, practice. Call non-profits, etc. to get pro bono work for some solid testimonials, start a website, and refer ppl to it. Also, think about a specialty- health care, fitness, industrial thingymajingies, etc. Knowing a particular market really well seems to be the way to go but isn't required.
A good place to start (at least for me) is businesses I already know well and have belonged to as a customer. For example, I just wrote a full-page mag ad for a kickboxing instructor I've known 7 years and whose gym I belong to. I know his problems, know the market (more than other markets, anyway), and it's great experience. Day cares, gyms, clubs, volunteer groups... work the existing connections and branch from there. Of course, this is one of a million ways to start. If it's working now, keep it as is.
Hope this helps,
Alex Stiner