Typically I would ring twice, or ring once and knock once if I didn't hear the doorbell. I have worked with people that would knock on the doorframe, very hard so it would go through the whole structure. I hated that. I would knock lightly enough to have the bare minimal chance of the householder hearing it, and try to leave before they had a chance to respond.
I like the idea of dummy-ringing the doorbell. Problem is, the witlesses I worked with wouldn't let that go. If they didn't hear the bell (and some of them were deaf and couldn't hear it even when I heard it clearly), they would have me knock (and hard enough so that there would be a chance for some ugly guy from upstairs to come to the door). In my old congregation, dummy knocking did not work.