If you're too frightened or lazy to canvas, you can re-leaflet the same areas you've re-leafleted before.
Also, ask your existing customers - every-one-of-them - to recommend you to their neighbors and friends. I'm assuming you do a good job and aren't extortionate (sloppy work and high prices come with experience

), so just say to them when you have contact with them, 'If you like what I do, I'd more than welcome you to reccomend me to your neighbors and friends'.
Don't offer them any financial insentive though; I don't think that's needed; honest.