At the top of the list is: Don't take a break from the game. Immediately you're off your game. In his interview with Charlie Rose John Heilemann observed, "She [Hillary Clinton] was very rusty." Here is a video excerpt of that take, captured by Politico.
As we all know, skills atrophy. That's why it's smart for the newly jobless to jump right back into working at any job. Otherwise they lose the ability to navigate the ambiguities of the work place. In public speaking, those who haven't been up there in a while lose touch with their gut instincts about what is effective with audiences.
For that very reason, Dale Carnegie training has students delivering one or more talks every week of the instruction. A useful follow-up to that is joining Toastmasters. Most cities have a local branch of Toastmasters. Here in Tucson, Arizona the group meets before the workday gets started.
The next lesson is stay open. That is, stay human. Obviously, Clinton pulled down the drawbridge and stocked the moat with alligators. No one could bypass that to the human being. No matter how brutal the situation we are in during an interview, including for a job or client assignment, we can't lock ourselves inside ourselves.
The third lesson is not to try so hard. Watching and listening to Clinton wore us out. Great performance art, including in politics, is effortless. The great performers include Ronald Reagan and Warren Buffett.
Of course, Clinton, just like all public speakers, can bounce back from a few bad days. The trick is: They have to be willing to learn from mistakes and do immediate course correction.