[A user of Essential Elements of Public Speaking thought that these concepts should be discussed in the text; I had omitted them because of space limitations. So, I post these very useful concepts here.]
When you have the opportunity to persuade your audience on several occasions (rather than simply delivering one speech), two strategies will prove helpful: the foot-in-the-door and door-in-the-face techniques (Goldstein, N. J., Martin, S. J., & Cialdini, R. B. (2008). Yes! 50 scientificaly proven ways to be persuasive. NY: Free Press.)
As its name implies, the foot-in-the-door technique involves requesting something small, something that your audience will easily agree to. Once they agree to this small request, you then make your real request. People are more apt to comply with a large request after they have complied with a similar but much smaller request. For example, in one study the objective was to get people to put a “Drive Safely” sign on their lawn (a large request). When this (large) request was made first, only about 17 percent of the people were willing to agree. However, when this request was preceded by a much smaller request (to sign a petition), between 50 and 76 percent granted permission to install the sign. Agreement with the smaller request paves the way for the larger request and puts the audience into an agreeable mood.
With the door-in-the-face technique, the opposite of foot-in-the-door, you first make a large request that you know will be refused and then follow it with a more moderate request. For example, your large request might be “We’re asking people to donate $100 for new school computers.” When this is refused, you make a more moderate request, the one you really want your listeners to comply with (for example, “Might you be willing to contribute $10?”). In changing from the large to the more moderate request, you demonstrate your willingness to compromise and your sensitivity to your listeners. The general idea here is that your listeners will feel that since you’ve made concessions, they should also make concessions and at least contribute something. Listeners will probably also feel that $10 is actually quite a small amount considering the initial request and are more likely to donate the $10.