As has been mentioned, it's really all about driving interested people to your site in the first place, the technical side of things are called META tags, if you look at someone's web site in code view you'll see that they add relevant information inside those tags i.e. "Window Cleaner"
So when someone searches on the web via google, the google spiders that crawl the web should hopefully have indexed your site as relevant to them and show it.
Paying someone to do this properly is the best way to go, but that's not to say you can't do it yourself or have other key words added to your META tags at a later date. If you add services to your work then make sure the people that are looking after your page can update them for you.
You can also setup free pages for your business on Face Book, then if you wait a few weeks they will likely send you a free £25 voucher to use on the Face Book site to promote your page and external web site. It's handy for free I suppose they have sent me two so far

Plus Face Book should display your adverts to people in your area as they monitor things quite well, I'm also fairly sure they use google cookies on your PC to display your site to people that may have searched google for a window cleaner at some point. It's a bit of a black art sometimes, but you'll notice it happening more and more these days.