Practice
Write the opener you will actually say, then drill the lines people use to end the visit.
Say this, then stop
Hi, I'm your name with Streetcanvassers. We're talking with neighbors about the issue you came about. Do you have one minute? The ask is the one thing you want them to do. If now isn't good, I'll go.
Read it out loud once before the first door. In your head does not count.