Work with your available light. Concerts provide some amazing opportunities for using light to highlight your subjects and make them pop. If you'd like examples of my personal work you can follow the link in my sig, I don't want to clutter your thread. Don't get trapped by cropping so tightly on your subjects. Find some space to work with on stage to really add some drama to the photo. Use the light to your advantage. A couple of these are pretty underexposed. Find ways to put yourself in positions that work to the venue's lighting advantages. If you're at a venue with fancy light, use it. Chances are good that most members of the bands find themselves lit up and highlighted in ways that draw the eye very well. Use that to your advantage.
Don't ever stop shooting at a concert. If you're looking for a specific shot, you'll need to stand there clicking away and being patient. If you have more of a vague idea of what you're looking for, keep shooting anyways. Concerts are the types of volatile shooting environments where it is too easy to miss the absolutely killer shot.
Don't cut off limbs, or instruments when cropping or composing. Also, don't put yourself in positions where the microphone could potentially cover up parts of a musician's face. We want to see the star, not the microphone.