I am by no means an "expert" on this subject. By no means at all. Not even close. My experience consists of a couple years in wholly insignificant bands. Nonetheless, it underscores my point to show that despite my significant inexperience I have still fully grasped these crucial, basic points. You should too.
If you are in an aspiring band or are simply an aspiring youngster looking to get in the game, the following list should be read and followed exhaustively. Do not pick-and-choose certain points to follow while disregarding others. Trust me, you will benefit in the long run by taking these points to heart. Ready? A pencil and scratch paper may come in handy.
1. Buy some fucking gear. If you are a guitarist, this means purchasing a "guitar" and "strings." In most instances, you will need to run your guitar through an "amp" (conversely known as a "head") and "cabinet" or other loudspeaker.
Drummers should invest in a "drum set" complete with cymbals and all stands necessary to support said equipment. While you may think it is cute/thrifty/etc to constantly borrow gear from other bands with whom you will play, I cannot disabuse you of this notion strongly enough. Drum heads wear out. Guitar strings break. Cymbals crack. Speakers blow. Tubes burn out. In other words, using other people's equipment costs them money. This will make the lender of said gear angry with you.
He or she will most likely lend you whatever you need but also resent you, think you are a dick, and probably never want to deal with your band again. Now if you lose or break a piece of your own gear and ask to borrow a replacement in an emergency, that is acceptable. Showing up at a performance with nothing and expecting to mooch off of other bands is not. If you do this regularly, I (and everyone who has ever shared a bill with you) hope you contract something that makes it burn when you pee.
2. Re-read the preceeding point thoroughly. Ensure comprehension before moving on. Do you A) have gear appropriate to your role or B) understand the urgency of acquiring it post-haste? Good. I don't care if you're poor. You can still afford cheap gear. McLusky sold a hundred thousand albums on $99 Squires. Shitty gear > no gear.
3. Obtain the use of a vehicle large enough to move said gear. The average band is 3 to 5 individuals. Combined, you can go in on a $500 used van. Trust me. You can. It is amazing how much a small amount of maintenance and knowledge can keep a shitbox running. America is laden with Chevy Astrovans – the automotive equivalent of Terri Schiavo. Nothing on a 1993 Astrovan will work, but the motherfucker simply will not die.
4. You do not need a sound-check. Sound-checks are nice. If you can get one, great. Do not, however, demand one and/or inconvenience anyone else to get one. Petulantly demanding a sound check makes you look like a pompous, self-aggrandizing twat. You are not Spinal Tap and you are not playing Madison Square Garden. You are probably playing a bar with a regular sound guy who knows the place pretty well. Shut up and let him take care of it. If you find the stage sound to be intolerable, politely ask after your first song if he can make an adjustment or two. Unless you royally pissed him off by demanding a sound-check, he'll probably be happy to accomodate you.
5. Unless you are headlining, quite popular, or specifically asked to do so, don't play for a fucking hour. For 99% of the local/independent/garage bands in the world, 30 minutes (tops) will do just fine. Don't show up in a town where no one has ever heard of you, play first on a 4-band bill, and play for an hour. The other bands will hate you. HATE. The paying audience will get bored and wander off. This will make the other bands' hate increase exponentially. You will also cut into the other bands' time and possibly even push one off the bill.
Unless you have specific and justifiable reasons to think anyone in the venue actually gives a shit about you, 10 songs or ~30 minutes is plenty. Even people who like your sound are probably just patiently waiting for the other bands on the bill. Get over it.
6. Get your metaphorical shit together. Nothing – save for watching Ann Coulter take a runny, corn-laden dump – could possibly be more unappealing than bands who take 3 minutes between every pair of songs in the set, filling said minutes with tuning, random fiddling/noodling, and rhetorical gems like "You ready?
Ready?" and "How does this one go? I forgot how we start this one." And who can forget that old chestnut, "What should we play next?" Compile a list of songs in an appropriate sequence (industry lingo calls this a "set") and play it in 3 or 4 song bursts with little to no pause inbetween. Mixing less physically-demanding songs with harder ones will help your stamina. So will practicing, dumbass. If you find that you just need a break after every song, put down the goddamn Creamy Ranch flavored Bugles and get your ass in some minimal semblance of shape. If an ancient, bloated manatee like Frank Black can do it, so can you.
7. Tip the damn bartender and be nice to the local bands. The bartender will make sure you get taken care of financially and the local bands – provided they don't think you're total dicks – will save you a ton of money and offer you a place to crash. Don't blow it by going on an extended soliloquy about how much they suck, even if they do very badly suck.
These seven steps are not steps to superstardom. They are seven steps to everyone not thinking you are a complete asshole. Follow them.