My experience is more centred around photo passes. Start posting stuff you have done online. Write up some reviews of shows you have been to start building up a collection of work. With photos this is done by shooting smaller bands at venues that give you access with your camera gear anyway.
Once you have built up a website with a collection of work start approaching bands PR with a view to cover their band, run an article etc tell them what you want to do where the work will be outputted etc. Then hopefully because they can see your other work they will be more likely to give you access.
Like I said this is more the photographic process but its very much applicable to the press side of things to.