If you're coming into Friday Harbor from the greater Seattle area, you'll want to take the Washington State Ferry that leaves from Anacortes (~1-2 hours from Seattle). If you're taking a car onto the ferry, make your reservation early (link here) and buy your round trip tickets (link here) ahead of time. We recommend arriving on Friday, October 4 just in case there are ferry delays the day of our wedding, October 5. You can make your car reservation 3-4 months in advance.
If you're coming into Friday Harbor from the greater Seattle area, you can also take a flight into the Friday Harbor Airport from Paine Field (Everett) or Boeing Field (Seattle) or you can fly into the Friday Harbor Marina from Lake Union (Seattle) or Lake Washington (Kenmore). You can book your flight via Kenmore Air here.
If you're coming into Friday Harbor from out-of-state, fly into the Seattle-Tacoma International Airport and take a flight through Kenmore Air or Washington State Ferry from Anacortes. More about that above.