And above all make sure that people out there are supported in singing along with you, by clear signals and encouragement. There is nothing worse than asking people to sing along and then making them uncertain about when they come in, or who does what, or you wander away from them, or change the tempo, or you screw around with the words, or try to do a fancy harmony on the first chorus break, or let them fade away while you go on or you stop abruptly. Or not thanking them. Or making them feel that you are using them to get yourself more applause at the end. These are all horrible sins, committed all the time against innocent audiences who have done nothing wrong.
If you get a chance to hear a Pete Seeger record in concert (and there are lots), you can learn a lot from the master!
Yours, Peter T. (audience member and long time sufferer).