'If you haven't been doing this, try it. Sing the song beforehand - while driving the car, while doing the dishes, while in the shower. That will show you where the tricky bits are.'
Trouble with this is I can convince myself I've forgotten it as I can come to completely no idea what's next, same with trying (against another song being sung) to scroll through the words just before my turn. This is just like seeing say a hydrangea yet being completely beat for knowing what its called.
I have announced once 'look I've no idea what the second verse is but this is what I want to sing because...'. Result; not a hiccup when actually singing the song.