Words matter. Believe it or not, voters listen. So when Barry Goldwater accepted the Republican nomination in 1964 with the assertion that "extremism in the defense of liberty is no vice," it thrilled conservatives but repelled moderates. One reporter summed up the moment's surprise by saying, "My God, he's going to run as Goldwater!" (Is there anything Mitt Romney could say which would prompt an exclamation of "My God, he's going to run as Mitt Romney!"?) And while George H. W. Bush's challenge that Democrats should "read my lips: no new taxes" helped him win in 1988, it cost him dearly in 1992—after he had raised taxes.
Introduce yourself. Especially for a non-incumbent, an acceptance speech is a critical opportunity to situate oneself in the American story. "There ought to be some kind of unity between your story and America's story," says former Clinton speechwriter Jeff Shesol. "It is very much about positing yourself as the man of the moment." In 1960, John F. Kennedy used his acceptance address to sketch out "a new frontier" and explain why he represented the new leadership needed to take America into it. Likewise George H. W. Bush's '88 speech effectively painted the nominee as being "symbolic" of the postwar American era—and in doing so neatly reintroduced an incumbent vice president to voters.
Know when to shut up. When Arkansas Gov. Bill Clinton placed Michael Dukakis's name into nomination in 1988, it took "33 minutes that seemed about five times as long," Time later recounted. That he got his loudest cheers with "in conclusion" was a pretty sure sign that he had droned on for far too long.