>>3247966Bigger venues with bigger bands you'll most likely need to get a photo pass. Need to be affiliated with a webzine or have a blog or something like that. Email the bands or band manager about possibly getting a photo pass. You will most likely be beaten half to death if you use flash in these situations.
Small venues with small/local bands you should be able to just walk in and take pictures. People probably won't care if you pop a flash here and there. Just don't over do it.