My advice to the inexperienced is "get the key right". Practising quietly at home will mean you find yourself singing in far too low a key when you take your song out in public. Your audience may not be able to join in that chorus you've practised so hard. Practise in the highest key comfortable for your voice and remember it so you can ask for a note if you need it!

Also, pitch the song so you can manage both the top and bottom notes comfortably. Some songs start low and then shoot up, leaving you with nowhere to go. Just think about the key before you start. New, unaccompanied singers can make a real hash of this.

And then - just enjoy yourself and the audience will as well.