honestly it beggars believe sometimes!!there was no internet when i started up in 1993 to ask "whats the best way of getting customers?"
canvass every week for 6 months 4-8pm evenings/10am-5pm saturdays.
knock on door and ask" do they want a good reliable window cleaner"if no move on to the next house, if yes give them a price/frequency/payment methods etc.SIMPLE!!
you might want to get some business cards printed up to hand out to potential customers.you could try leaflets but you will have to drop a hell of a lot to even get 10 customers!!
much better to canvass!!also dont take any notice of the signs people have on the doors saying "no canvassers!!".just knock on anyway!!!

having a sign written van and putting a leaflet/business postcard in the local shop/garage should help as well.the local parish magazine could be an idea.
most of my new customers come from word of mouth and recommendation with the odd one from my van and card in local garage!!

hope this helps!!
dazmond