two_planks,
Start here first
http://www.dol.wa.gov/businesses.htm. This is Washington states dept of licensing (DOL) business website. It will actually walk you through 90% of your business license questions.
Essentially you need to apply for a master business license to start work. Depending on your business structure and the specific work you want to do there may be other licesnses or registrations that you will need. If you are going to incorporate, you'll need to apply to the "secretary of state" for corporate status. Some businesses require a contractor registration issued by the Washington dept of Labor and Industries. Btw, Dept of L & I offices are set up to take master license applications and collect fees. If you're going to have employees, you'll need to notify the Internal Revenue Service (IRS). Additionally, some cities require you to purchase their jurisdictions license.
I know it looks bad, but its not as bad as you'd think to go through the process. It does cost a few bucks the first time, but renewals are much cheaper. Let me know if you have any questions and I'll do what I can to help you out.