Make sure you put your full name and address on it as well as your home phone number. It really works because people need to know who you are and that you are basically honest and trustworthy. They have to be sure you are not casing the place for a buglary or that you are some mad axe killer.
I have had so many customers comment on the fact that I do it and thats why they rang me.
Had a leaflet through our door from another window cleaner a couple of months back, it just had "ring Steve and a mobile number". Looked dodgy to me so it would look dodgy to the customer
We use bright orange paper, seems to work best.