Allow plenty of time to set up so you can chill for a bit before you start, or help out a bandmate who's having issues. Nothing worse than rushing to set up and then having to launch straight into your set without being happy.
Nerves are good but don't let them get the better of you, it's supposed to be fun. If you find it particularly difficult then take on the role of a character, then it's your character up there doing it, not you.
Play the rock star (to a degree), look confident, have a bit of swagger. Move more than you think you should, movement needs to be exaggerated to be noticed on stage, (a video of you will prove this).
If you mess up, keep going. People really don't notice as long as things keep flowing.
Try to relax and make a conscious effort to keep to rehearsed tempos. Once the adrenaline kicks in your 45-50 minutes of material will end up as 30-35 minutes.
Keep any messing about between songs to a minimum. If the singer is good working a crowd then fair play but band members looking at each other, constantly asking "are you ready?" looks bad. Agree that you will launch into the next song unless someone says they have a problem.
Above all, enjoy it. Energy flows both ways. If you (the band) look like you're having fun then so will the audience. If the audience look like they're having fun then that will feed your confidence and make you perform better. The energy continues its circular flow.