Whtever you feel comfortable with, don't sound contrived. Eye contact. I leaflet a couple of days before knocking, then they know to expect someone and I start by asking if they've read my leaflet. If they say yes, I then start my pitch, if they say no, I still start my pitch. They're at the door, ask them if they want a good reliable windie blah blah.
The more you knock and ask, the more custies you get, and the better you get at handling rejection. It's being able to handle rejection that gets you more work then the guys who fold at the door and go home. Simple when you think about it.
My competition near me can't handle rejection. One of them goes around every month sticking a note on each door saying summat like "We're cleaning windows in this area tomorrow for X amount of pennies, if you'd like us to clean yours, please tick box"
Haven't lost a single custy to muppets like that yet. If they door knocked, then they might actually get some work. Same guy tried leaflets a year ago. Crap self typed in different fonts all over the hand cut bits of paper. Even offered to weed the path at each visit!!! Some people would rather eat their own foot cheese than knock a door!!
Worth remembering maybe.