Things to know when you start playing in public, but no one ever tells you.

[PingJockey]

Tune your guitar. Seems so obvious. A couple of weeks ago, I went to a concert with three famous singer/songwriter/pickers playing round robin fashion. Two of them had at least one string out of tune all evening. To my ear it really detracted from their performance. The one who was always in tune checked his tuning between every song.

Make sure that your guitar is in tune with itself. Check it with your electronic tuner, but also make sure that all the E's are in tune with each other and all the A's and all the C's, etc.

The trick I learned is to tune the low E string so that the tuner indicates that it is in tune just as the sound decays. Then check the G note on the third fret and adjust so it is in tune also. When they are both in tune, go on to the A string and tune it for A and C. Then do D/F, G/A, B/D, E/G. After you have tuned all the strings, go back and recheck them as changing the tension on the neck can affect the tuning. Now play E on the E, D, and E strings and listen for a beat wave. Check again with A, C, and other commonly played notes.

[SteveHung]

Make sure you know the "happy birthday" song. Sometimes, you'll be playing in public, and it happens to be someone's birthday, and their friends walk up to you requesting you to sing happy birthday to their friend.

[Davis Webb]

Most people arent going to listen to you. They are in the club to drink and hook up.
Go with it, at least you have a gig