if you've an eye catching and nicely sign written van, park in a prominent part of your home town each morning and go for a coffee, or aim for a shop or business on the high street and clean as people are on their way to work. its free advertising innit?
over time , people notice
"why just have a tel number that no one will ever remember"
not a dig ww , glad it works for you, but most people have mobile phones these days, its easy to punch in a number and save it!
I dont have a website so can't comment on that, but when i've needed a trades person I've usually gone to someone i see around a lot. Imo I don't think potential customers trawl the internet looking for a window cleaner (its low on their priorities) but when the opportunity arises and they see your van or you working they then ask for a card or take the number down.
I made a lot of mistakes when starting up and spent money in various ad papers and local directories to very little success.
Being seen has been by far the best advertising for me, recommendation incentives to your existing customers by way of a discount has worked as well.
Simon