If a book is used, have the song you're going to sing bookmarked so you don't waste time shuffling through the pages when it's your turn. It's baffling sometimes at a singaround, when everybody can tell when their turn is coming up, that some people start futzing around with their songbooks or notebooks when it gets around to them instead of having their chosen song ready. I'd rather people refer to the lyrics if it is helpful, and it needn't detract from the song. Sometimes a book or lyric sheet just serves as a 'safety net' and it isn't even necessary - but the security derived from having it helps ward off nervousness.   It's well known that a song one can sing perfectly at home or in the car can fly from memory when you're in front of an audience. And I agree about noting the key, etc. I always have a set list with the keys noted, and sometimes some notes about the songs, as one poster noted - in case someone asks.