Depend on which lens you have. Try to use the Mmono pod too (you can't use the tripod in most the concerts).
For camera, set the ISO Speed to 800 or high;
Shooting modes: Manual (Using the center weighted average metering to check then set with manual exposure), or AE ( Aperture-priority ). Check the shutter speed to see you can set it as high as you can, like 1/125 sec (high is best), the rule is for example 200 mm lens you need set it to 1/200 sec w/o IS or tripod.
Manual focusing (switch on lens) because sometime the autofocus don't work well in the low light condition.
Metering modes: Center-weighted average.
White Balance: Tungsten (don't use the auto white balance and remenber change back to auto white balance after the concerts ).
Drive modes: Single.
For lens, set it to manaul focusing, and the bigger aperture (lower number F2.8 is better than F3.5 etc).
Before the concert start, take the pictures to test the setting, also test it right after the concert start, and injoy it.