Commonplace: the result of combining a cliché and a stereotype. Even though I hate both, Heinrichs does make a point. Commonplaces vary but so should the settings.
So I found a video which talks about rhetoric, jokes (this includes witty, facetious, and urbane humor), and commonplaces. Particularly the misuse of commonplaces. This man is witty. He says that if congresswoman Maxine Waters knows what happened to Whitney Houston she should "step away from the crack pipe, step away from the Xanax, step away from Lorazepam because it's going to get [her] in trouble." This is what results of congresswoman Waters calling Republicans demons and gangsters. Who failed with the commonplaces and is out of decorum now? I'd say both of them! To address and audience one needs to have a little background check on them. Had he been talking with friends the comment might have been funny but this comment on national television is a whole other level.
If people babbled, or repeated the same thing over and over about Maxine and one were to use that commonplace chances are your audience will reject you. Why? National television addresses a much to big audience and it's hard to win so many people. Commonplaces appeal a great majority of the people (thus their name) but there are too many opinions the speaker would try to mould. Here's where you need to find the broadest context, to define how to convince as many people as possible.
Other than humor and commonplaces one can give the audience facts and data. Logos, duh. This is called stance. The video teaches one how to convince your friends to vote. One has to use lots of rhetoric to convince them, especially facts to convince them voting is the right way to go.