Its also good to mention that you live on the estate (if you do!!) as customers seem to respond well to that. I live on a large new estate and if a customer is a bit hesitant and unsure when I knock on the door I mention that I live around the corner at No. 6 and there faces light up. Its almost as if that makes me more trustworthy!!!
Another tactic I have and it works well is knock on the door, If there is no answer and if it is possible, look over the back wall and do a quote for the house. Post it through the letterbox and call back a few days later and simply say...'I popped this leaflet through your door with a quote for £XXX for getting your windows cleaned and was wondering if you would like to take up the service?