If you have a regular customer on a street, flyer the rest of the street every time you are there.
It amazes me how many times I hear "I have been looking for a window cleaner for ages" when I know for a fact that I have put a flyer through their door every month for the past year.
that gets me aswell, i leafleted a certain street found out the wc had died a while before i dropped leaflet and got 1 custard come out and say i need a wc,since then iv picked up half the street as they seen me cleaning and said same thing,just goes to show with door knocking i would have picked these up a long time ago
i would say drop them every 6 months else you will be spending a heck of a long time just dropping leaflets through same doors,i personally couldnt be arsed go back to same place again