just to reverberate what has been said . BE PROFESSIONAL. thank them for their time. whether or not they say yes. even if they say yes thank them for their time. remember they are giving us the privilige of hunting thier property and it can be taken away. so even after you get permission keep up the relationship. dont get the yes and then never make contact again. if you get a yes and kill something offer them some of the meat or even offer for them to come over for dinner.
be ready for some no's. i was turned down by a neighbor but we ended up having a good conversation and still keep in contact. one day he might change his mind.
One thing i have used before but only do it if asked. is a liability release form. one of the big reasons poeple dont let us hunt on their property is fear of us getting injured and sueing them. so i got a liability realease form and sign it for them releasing them from any liability if something was to happen. just make sure you have your own insurance coverage if you do this.