John
When I first started out in 1990 I had no existing customers to fall back on and had to go door to door.
Here's what worked for me;
Target a neighborhood that needs your service, not just one house in the middle of nowhere but a sub division with a couple of hundred homes. If you don't have subdivisons like that where you are just pick the largest one you can find.
Go on Saturday when the guy is usually home and you're not spooking the wife or kids by just showing up.
Find a house on the corner or one on the entrance road to the subdivision.
Tell him you'll clean his roof for FREE and I mean FREE no strings attached and no charge, period.
All you want from him is to let you do it on a Saturday and to flyer up the neighborhood before then to let everyone know about your service and the upcoming job.
Put a sign on the front lawn a week before you do the job saying "watch this roof, Professional roof cleaning to be done this Saturday"
When Saturday comes put on your best work clothes, have the truck washed, look professional and do the FREE job.
Take before and after photos and then hit the neighborhood again with another round of flyers using the photos.
I did this with my housewahing company in over 12 neighborhoods and I "owned" the neighborhoods! I got over 65% of the homes in any area I targeted and still use this method today.
It's faster, easier and less expensive then door to door and there's no postage fee. Just get your kids or someone elses kids to hand out the flyers.
A word of caution, check with the town you intend to do this in to find out if they have solicitation laws and if you need a permit to hand out the flyers.
Never put them in or on a mailbox it's againt the law.
Good luck