Being in a band and not promoting it is like having a business and wanting to keep it secret. You will not succeed and no one will know about your band unless you promote it... and my advice is to promote it like a business and run it like a boss.
It's not a booker's job to get people in the door to see YOUR BAND. It's their job to book a solid show with good bands that promote themselves, work out the ticket prices, make sure the security and sound are locked in and advertise the show by using the venues advertising budget or their own to do so. No one cares about your band as much as you do, therefore no one will kill for your band but YOU. Unless you're paying said promoter to promote just your band its their job to promote the club/venue. So don't sit around bitching about promoters/bookers not doing their "job" promoting your band when that's your job.
If you feel a booker/promoter isn't doing good enough, then do it yourself. Go direct to the venue owner/manager and try booking your own show.
It's not always as easy as you think.
Merch is key to making money. DUH. You have to sell shit to make money.
You should have shirts, cd's, shot glasses or whatever to sell at every show. If you make unique flyers for your shows (like we do) print out larger size versions and sell them for $2-$5. We made poster sized flyers had them mounted on foam core and made anywhere between $15-$40 on them.
This helps when you get stiffed by the venue or booker/promoter for payment or when you play a free show.
Set up a Paypal account for the band and get a credit card swipper so you can accept cards where ever you are.
You also need free stuff like stickers, picks, etc for the broke people.
OUT OF THE BOX THINKING:
Being an advertising professional I have to think of out of the box solutions for clients who are looking to stand out in their field. It's the same thing we need to do as bands. If there are 3 or 4 other shows the same weekend we're playing a show we have to come up with a unique theme or incentive to get people to our show, like a car dealer during a holiday weekend.
Facebook invites aren't the only way to promote shows. There are thousands of internet radio stations that cater to unsigned bands as well as blogs. Get those people involved too. Give away a spot on your guest list as an incentive or host a raffle where a winner can get a bundle of merch from all the bands on the show that night.
Most bars have alcohol vendors that would be willing to help pass out flyers if you throw their logo on it.
These are just a few tips from my experiences. Get out there and find your own unique out of the box ideas.
Look at what small businesses are doing to draw customers.