I had no idea I wanted to be a concert photographer. I liked taking pix of mushrooms in the woods and my dogs and that was about it. I smuggled a 7D and 70-300mm into a festival once and took some photos that were shared with the festival's marketing director and got an immediate offer.
A tangent, but an important one - the next step was to sell all my lenses and buy f/2.8 or better. Costly, but fortunately my f/4 lenses sold quickly and without significant loss.
From here it's important to focus on making your work visible. As you grow it becomes more than that, you will need cart if you plan to sell, clients may need image proofing, digital downloads, etc.
Last is the business side. It's complicated and extremely difficult to grasp, and sorry but I can't help. Most of my financial arrangements are standard but many are completely adhoc. But it's very, very important you move to the point that you are not whoring yourself out. You'll find that it's not good for either you or your peers, and the practice of shooting for free is killing the industry. Everyone starts off photographing for free, just don't stay there once you've shown your value. </soapbox>
Get it all together, then start reaching out to publications and band management. Become affiliated with an e-zine, stick with them until you grow and find another. And keep moving up. Have goals, talk with peers, study the work of others, differentiate. Respect artists, other photographers, security, sound and lighting crews, production & tour managers, become friends with them all. Never, ever release an unflattering photo.
It's easier to get into a venue via a publication. I prefer to go directly through artists (unlimited access, backstage, onstage, drink their beer, blah blah), and if it's a show and performer I'm interested in I contact their management, usually not until 3 weeks before a gig, and offer my services. If they decline to pay I then go through publication. Legitimacy is key, it will take some time.
I'm no pro by any means, and am still evolving so take everything I say with a grain of salt . I've made a lot of contacts and learned a lot from pros, and I don't expect the evolution will ever taper off.
I was once an actor. Photography self-promotion is just slightly less demeaning. Stick with it, if you're good the humility will pay off.