The first "governmental" step (there are many first steps) when starting a 501c3 non-profit organization is to incorporate. Like a profitable corporation, your organization will possess all of the same rights and protections. In order to become incorporated, you need to file Articles of Incorporation with the state your organization wants to do business. This is a simple form and does not vary from state to state. The form needs to be mailed in with the appropriate payment amount. You can find this form on the SOS website.
Once you are incorporated with your chosen state, you need to apply for an EIN, an Employer Identification Number. You can apply online during business hours @ www.federaltaxid.us/irs/sim.asp
OR obtain form SS-4.
The differences between states is marginal at best. The non-profit corporation laws are dictated by a model set of laws that most states develop. Generally, it is best to simply organize in the state where you will operate and where the directors are located. This way you avoid multiple state registrations, fees and taxes.
That all being said, Washington state has a great non profit community. You will find that your organization will be well treated here.
To help you get started - i pulled the blotter from a recent post put up by our non-profit guru in our office:
The EIN number is effective immediatly and is needed for most of your business needs, including opening a bank account, applying for business licenses, and filing a tax return by mail. Take note: Your application will take up to two weeks before your EIN becomes part of the IRS' permanent records. You must wait until this occurs before you can file an electronic return, make an electronic payment, or pass an IRS Taxpayer Identification Number matching program.
Next, File for 501c3 Status by obtaining a 1023 application from, http://www.irs.gov/pub/irs-pdf/f1023.pdf
and Publication 557 (document is 72 pages, the form is on page 68) from, http://www.irs.gov/pb/irs-pdf/p557.