Flair for stage performance is really something that cannot be taught. But still here are a few tips I think help on-stage:
1) Be relaxed. If you are nervous it is going to show in your playing. You have to be calm and collected to put on a good show.
2) Do not do nothing on stage besides playing guitar. This may not be so much of a problem if you are singing but I have seen countless rookie guitarists staring at their guitars for a whole hour without looking at the crowd even once. Remember that you are playing for the crowd not for yourself and try to involve the crowd as appropriate.
3) If you are a vocalist you have the added responsibility of getting the crowd to join in with you whether it's singing or screaming. A crowd loves having a good time at a rock show. It's upto you to give it to them.
Since the creation of the Internet, the Earth's rotation has been fueled, primarily, by the collective spinning of English teachers in their graves. (QDB #754533)