MYTH: Bands are "Discovered".
FACT: Work your collective arses off, but still have fun with it. Promote yourselves every way and anyway you can. MySpace and Facebook, love 'em or hate 'em, are your friends.
DON'T: start out playing originals. Cover the bands in your genre who really know how to write good songs. Learn your parts well. When you get good at this, cop the best stuff and write your own material

Covering songs will develop your sense of timing, song structure etc.
DO: put together a good demo of your best stuff (3-4 songs) and hand deliver it to club owners, promoters etc. Check around, your town may have someone organizing all-ages gigs that will put you on the same bill as more established bands.
DO: be a sponge and learn all you can about the "biz", even if your goal is to just play backyard parties, be the best dang backyard party band in town.
DON'T: **** away and show off what an awesome guitar player/bassist/drummer you are.
DO: serve the song or the performance. That means everyone must play their part, even if it's hanging back a bit (see "wanking" above)
DON'T: start a practice with everyone in their own little world playing a different song with the amps dimed. It sounds like crap, everyone will think you suck, and the neighbors will complain.
DO: wear earplugs, especially at concerts/shows. I've helped run sound at a couple of local all-ages punk shows here and everyone wants to run their Marshall stack on 11 :thwap: (see "wanking" above)
HAVE FUN! :rockon: Learn your craft. Self promote. Enjoy the ride, wherever it may take you.
Trev