If you are canvassing to an elderly couple or person, the deal changes quite a bit.
These folks have been through numerous campaigns in their lives, and many are used to the "old-fashioned" way of canvassing. If you do not pay respect to this simple fact, you'll give them literature and be on your way. Or, they'll see you and not answer the door.
A good strategy that I've been using to canvass the elderly in my precinct involves the following: Shirt, Tie, Jacket. Name tag. Ron Paul button. Since I have a crew cut, I wear a cloth driving cap which is a design I've seen many elderly gentlemen wearing around the neighborhood.
I ring the doorbell and stand at least 5 feet away from the door, even if that requires me to go down steps. If the door opens in a minute and the homeowner(s) appears, my script goes like this:
"Hello Sir/Ma'am/Folks my name is Dr. X and I'm volunteering for a political campaign. I have some papers that you might find to be of interest - did I catch you at a bad time?"
From there, if they are interested they usually ask about one of my keywords - "which political campaign", "what are the papers about?". Then I'll tell them the information they want, and try to engage them in a little light conversation while I'm getting their hand-out.
If they aren't interested, they'll say "it is a bad time". Then I'll say, "well here are some things you might want to examine when you have a chance, sorry to interrupt your day".
It is as simple as that.