1. Plan for failure.
I would wager that the average comic-run show in a bar lasts, on average, no more than five shows. In cities such as New York, L.A., and even Chicago, shows come and go with such frequency that comics themselves cannot keep up. Bar shows are tremendously difficult to run -- you need to attract an audience, book the shows, rely on comedians to show up, and satisfy the owner and potentially other customers who didn't know about and/or are not interested in stand-up. Bar shows always seem like a great idea, to your friends, yourself, and the bar owner, and getting a crowd on the first night can be relatively easy. What is more difficult is getting a crowd on the second night, and so on.
So, work hard at the show, but don't invest too much in it. You don't need a website, or professionally produced flyers, or a $200 budget for a solid headliner. Start small, and if you can build a buzz, go from there.
2. It's not an open mike.
Maybe it is, really. If you want to post on the local standup message board or Craig's List that it is, that's fine. But don't advertise it as such.
3. No improv.
Improv sucks. It really, really sucks. This isn't really relevant, but I've been in Chicago for a month and everyone keeps asking me if I do improv and I get really, really mad. If you do improv, I'm sorry. Maybe your group is actually good. But probably not.
4. The venue is key.
You need to have the comedy show separate from the rest of the bar. You HAVE to. The only exception to this rule is if the bar owner will let you man the door and essentially take over as manager of the bar for two hours, which is rare.
