Hi,

So, does that mean we should start with the following?

"I know this one very well, so ..."
"I'm not apologising for whatever is going to go wrong ..."
"Okay, let's give something old a try ..."
"I'm doing this one on routine ..."
"Here's a song I'm doing unrehearsed ; it's too easy ..."
"This didn't work at home, but well: Let's see ..."
"If this does work, I'll do another one ..."
"I'll always do this better than the original, so ..."


A lot of it is down/up to expectations, of course. Pete Seeger singing from a newly encountered song from a crib sheet does explain to the audience, even if that explanation slightly diminishes his standing; he dos so as his audience doesn't expect him to use a crib sheet. Still, whole orchestras play with paper in front of them without anyone expecting anything else.
Folktalker Vin Garbutt is expected to occasionally sing a song in between his spoken words, and if someone in the audience has different expectations, that person is in the wrong audience. But if you're playing background music, you're mostly expected not to speak at all.
Introducing "I don't know this one too well, but a young lady in the audience insisted I play it tonight." is much better than first confronting the audience with a song full of unexpected (by the audience) errors (by you), and only afterwards trying to make it right by an explanation.

Returning to Pete Seegers: Turn, Turn, Turn.

Bye,
                                                                Mysha