Thomson, Yell etc are ok to help you up google, but get an SEO company or someone who knows, to do a search dot how many times "window cleaner *your area*" gets searched.
In my experience, advertising is a waste of time and money, and hope.
Ranking high on google will see your enquiries increase, but what you tend to get is shoppers who want 3 or 4 quotes.
Do a good job, and you will get referrals.