It's relatively easy to file for divorce in Washington State, though there are some local differences from one county to the next. If you're in the position of needing to file for divorce in Washington State, you need only file paperwork with your local family court.
Complete a Summons, Petition for Dissolution, Confidential Information Form and a vital statistics form. All but one of these forms are available on the Washington State Courts website. The vital statistics form is for the state records when your divorce is finalized, and you can fill this out at the clerk's office when you go to file your divorce.
Find out what supplemental forms are required, if any. In some counties, you'll also need to fill out a cover sheet to clarify jurisdiction (e.g., which county or courthouse should handle the case) and identify the case type.
Take the completed divorce forms to the county courthouse. You'll need to present the original, signed forms to the clerk for filing. Keep photocopies of these documents because they will need to be served on your spouse in order to get the divorce started. You'll need to pay the filing fee, which can also vary by county, but is usually between $200 and $250. If you can show proof of financial hardship, the filing fee can often be waived.
Once you've filed the Washington State divorce papers, you'll need to have them personally served on your spouse. Anyone can personally hand the forms to your spouse as long as it's not you or a minor. Alternatively, your spouse can sign a form called an Acceptance of Service.
Washington is a no-fault divorce state, which means you won't have to say why you are filing for divorce. The petition only needs to include bare-bones information, and all you need to say is that "the marriage is irretrievably broken."
If your case is very simple, for example if there are no children involved, there is little property to divide, or if both parties are in agreement about the terms of the divorce, you can probably do fine representing yourself pro se. Otherwise, consult with a qualified divorce attorney in Washington State.