Research the venue. Find out if it hires live music, which nights it hires live music and what type of live music it hires. You will waste time and money trying to book a Friday gig for your Goth band at a jazz venue that only has live music on Mondays
Contact the right person. Never leave your demo and press kit (photos of the band, a bio, contact information and any press that your band has received) with the bartender, hoping it will find its way into the booking agent's hands. Find out who handles the live music at the venue, and make him your best friend.
If your band is up for it, try booking with a promoter. A music promoter will handle the publicity, the venue booking and will make sure everything goes smoothly. Find the names of local promoters, and send them your demo and press kit.
Sell yourself. The reason venues book live music is to make money, so let the person who hires live music there know that you'll do your best to fill the house. Offer to advertise, show him your 200 local followers on MySpace or tell him that you'll get your attractive female friends to sell tickets at the door.
Be patient. Many venues book months in advance; don't expect to drop off a CD and get a gig that weekend. Always follow up, but make sure you're not coming across as annoying.
Work out a deal with the venue. This should cover pay and accommodations for the band and equipment. It's always best to have any agreement in writing in case someone tries to back out.
Once your band is booked, make sure to play a great show. Bring as many people as you can, and don't leave the minute your band is done playing. Make sure the experience is as stress-free as possible for the people who work at the venue.