1. Expect to not hear yourself.
In all my years of playing every dive bar, bowling alley, and snooty wine hall in the land, the number of clubs with adequate stage monitor set-ups is exactly equal to the two shows I've played where I could actually hear myself. I ain't gonna tell which clubs in town you should avoid, though, because some of these places are still great clubs and all young bands really can't be choosy about where they play in the beginning anyway. Dues must be paid.
2. There will be tumbleweeds.
When your hard work, or networking skills finally lead to a high-profile gig opening for a name band whose gig is guaranteed to be SRO, do not EXPECT to play your entire set to a full house. In all likelihood, 75% of your show might be to the wait staff and the other band's road crew, but then with two or three songs to go, BOOM, you'll realize that there are suddenly a fuckload of new eyes staring back at you. Pace your set accordingly. In other words, don't blow all your best songs and stage pyro on a big entrance that nobody sees.
3. Dress for success.
If the clothes you wore to work are the same ones you're wearing onstage, there is something seriously wrong with this picture. Ask yourself "What would KISS do?" and get yourself some knee-high snake-skin elevator boots. Maybe I'm kidding, maybe I'm not, but if you ever wanna lose the day job, take some pride in your "night job" by wearing something that demands attention. That IS the whole fucking point, after all.
4. You're a rock star, not a door-to-door salesman.
Don't hype your band name, website, mailing list, or soundcloud page from the stage. Again, ask yourself "What Would KISS do?". How cool would it have been if, right before spitting blood and breathing fire, Gene Simmons stopped and asked everybody to stop by the merch table and sign their mailing list? If you're smart enough to put your legible band logo on your kick drum head (gigantic backdrops are still a luxury at this point) AND you rock everybody's pants off, FANS WILL FIND YOU.
5. Merch. All Night.
HAVE SOMEONE THERE TO RUN YOUR MERCH TABLE ALL NIGHT. Why? Because you want this to be the first thing those new fans see right after your set AND at the end of the night when those who came to see the headliner are on their way out the door. Do not tear down until the last fan has left. Also, pay your merch gal or guy well. The better you treat them, the better job they'll do, and the more shit you will SELL.
6. Find yourself a good sound asshole.
You talk to any now-legendary band from the Ramones (okay, that might be hard to do) to the Replacements to Smashing Pumpkins , when they were promoting their first major label album, their crews made more money than they did. While its not necessary to have your own crew starting out, go into your pocket to ensure that you have your own sound guy at every show. I'm talking a real sound guy, not your buddy Todd who winds up getting pushed around by the bar's default sound guy or the headliner's crew. Find the priciest asshole in town that you can afford and play that person with compliments, booze, and the promise of steady money (they won't believe you, but it will make them laugh).
6.5. If the show isn't worth bringing your expensive sound guy, then it isn't worth playing.
Taking this to heart will save you much heartache and that means everything when rejection and/or complete indifference is such a large part of the daily grind. Yeah, yeah, many a band has bragged about playing anywhere and everywhere that they could when they were starting out, but, these days, a YouTube clip of your band stinking up the joint is NOT gonna do you any favors and it will follow you forever.