I haven't done a proper leafleting campaign for a good while, mainly because of time, but what we have just started doing is a "5 & 5" policy which works well and targets areas where you are already covering.
When we are out doing a job (windows/carpets or whatever), if possible we drop leaflets in the five houses to the left and five houses to the right of the one we are doing.
The response has been better than excellent, got a 6/10 response from one drop within 3 days of delivering.
Another one we did went into the house of the manager of a local National Trust property, he rang us up and we have now got the contract to cover the janitorial duties at the property 3 days a week, plus holiday cover as well as the window cleaning contract for the visitor centre and the main house.
I've also got a meeting with him to discuss more specialised out of season cleaning of the house and main areas.