What I recall is that a large part of the show was him tracking down other standups and asking them about their experiences and any advice they'd have. (The documentary includes footage of him walking along with a young Woody Allen, talking about having to be born with an innate sense of humor and needing to be up on stage.)
One of those that Plimpton spoke with was Jonathan Winters. Now, clearly, anything Jonathan Winters would suggest to George Plimpton would be pointless -- or in fact, it would probably be pointless suggested to any human -- because what Jonathan Winters did was unique and pretty much likely fit only Jonathan Winters. But his suggestion to George Plimpton was especially pointless -- but very funny as a suggestion from Jonathan Winters.
He said that before the performance began, when the curtain was open and the stage bare, Plimpton should grab the curtain on one side with his hands around the edges, and ever-so-slightly peek his head around the curtain. And then, with a happy, oh-so-innocent filling his face, he suggested that Plimpton should say -- in one of those high-pitched, squeaky little kid's voices -- "Hi! I'm George. We're going to have some fun!!"
I would have loved to have seen George Plimpton open his standup act like that. In fairness, it probably wouldn't have hurt much. As you'll see in the documentary, it didn't go well. My recollection though is that he did eventually get a few laughs. But no much...