the write stuff
There's a common misconception that every journalist is a failed musician.This often holds true, except in the case of where failed journalists (eg. Bob Geldof, Neil Tennant, Chrissie Hynde) take up music. They had the right idea -writing about music isn't the fast track to fame and riches.
To make it as a music journo there are 3 maxims.
1. who you know
2. right place / right time
3. luck (can be generated via hard work combined with #2)
What about talent - or liking music you cry? Useful, yes, but less essential.
That may sound embittered and cynical, but it's tongue-in-cheek. Well, a bit. A good writing style is important, but equally important is stringing together a coherent sentence, staying in word count, toeing the party line, and not upsetting anyone. That's not a complaint as such, just common sense.

good technology
One day reviews will be all generated by computer (see our handy guide) but the PC has been instrumental in getting music writing out there.
Careless Talk Costs Lives, Bang, XRay, Word and Bullit have just joined Q & MOJO on the nation's shelves. As has is this music? Ahem. It might seem that all these are the answer to prayers of aspiring journos, but a common feature of these mags is the vintage of the contributors - many are refugees from the days of Melody Maker et al. See maxim #1.

what the kids are buying
'Zine' is short for FANzine - written by fans because they care about the music. Producing your own zine is possible with just a PC and photocopier access (though 'real' zines will utilise just cut-up letters and a handwritten scrawl).
If you have no photocopier then do a webzine. Sadly, the web's not an earner, so it's down to the paper press I'm afraid. Either way, if you're any good you can build a portfolio of different mags you've worked with.

writing to reach you
Approaching a paper for work is a bit like submitting a demo (for the failed musicians out there). So, call them up, find out who's the music editor. They'll probably invite you to send something (doubtless pointing out they have plenty of reviewers already.)
Keep your sample short - 200 words or so - as any work you get will usually be a short live review. (The editor will keep the record reviews to himself as he can knock these out without leaving the house and then flog the CDs down at Record Exchange.) For a mass-circulation paper make your piece on someone their readers will have heard of, or failing that, spell out how the band compare to Travis (possibly explaining who Travis are in the first place). Do think about the readership - swearing may carry punch in a zine but a broadsheet may be less open-minded.
Once you're done, spellcehck, then read it aloud to catch over-long sentences or repetition. - if you start to turn blue, punctuate. Maybe get a friend to check it for you. Finally, put your details on the letter or email (email is next-to-essential these days) so they can easily commission you.

submission (dragging me down)
In the unlikely event that the phone doesn't ring, call up a week or so later. If they've read it, it'll be a yes/no situation (or yes/"we'll keep it on file"). If they say no ask why not. A decent editor will at least give you pointers.
If they say it's crap, don't blow up; thank them for their honesty. Bear in mind that editors move between publications and they may eventually become your boss!

mass market penetration
There's a 4th maxim - perseverance. Hard work will eventually put you in the right place at the right time. Personally I've picked up work when someone was on holiday (the deputy went a bit wild with a fortnight of underground reviews!); another time the editor turned out to be a fan of the Butthole Surfers (who were in my 'portfolio'.) But be prepared to work for free, especially during the Edinburgh festival ! You're unlikely to top 10p/word anyway unless you get into the tabloids. And don't let rejection get you down. One editor has a reputation as a power-crazed control freak. He will rip your first piece to bits, just to show who's boss, but if you can swallow your pride he won't even check your work again. Generally editors are too busy to come up with all the ideas, so 'pitch' them something.
And if you run into Michael Jackson in the pub, grab your chance - you might not get another one.