The secret of a good singaround is to invite Steamin' Willie!

Joking apart, the secret is to realise it is about participation rather than artistic merit, and everybody has a part to play.

That said, the posts above regarding some of the stereotypical participants remind me of why I sometimes nip to the bar and forget to come back, sorry..... (Not that I am much better, but you don't have to be a writer to be a critic.)