SMILE!
Big cheesy one otherwise you can’t see it from more than 10 ft away. Makes you look like you are enjoying yourself and if you look like you are it helps the punters enjoy themselves too. Doesn’t matter if you don’t feel like it but every ‘concentration face’ (that you (anyone!!) would naturally make) will make you look moody & distant.
I’ll echo look just over peoples heads until you feel comfortable to actually make eye contact. People will still think you are looking at them and feel ‘engaged’.
And, above all, have fun…
You will smash it!