Scott gave a terrific answer. I would add that positioning is key, know who are you and your value prop and stay focused. It's easy to take on a search for anything, but the more you do that, the harder it will be to build a track record. Even in tech, some of the best engineering staffing firms don't do everything within tech, so they'll turn down a help desk req or peoplesoft consultant search to stay focused on software engineers, etc...

There is also room to run in the contract staffing world, the residual incomes are usually much better in the long run than perm search, although barrier to entry is a bit higher. You can usually pick up some payroll deal business after establishing yourself.

Good luck!