For those of you just starting out, be prepared to start off playing Sunday through Thursday. Try not to be too disappointed if the first night a buyer offers you is a Tuesday night. Do your best to promote your gig (coming to the Social and talking it up and handing out business card sized flyers is one great way to do this). Make sure that you send your show information to the local radio shows at least a week before the actual show. Lots of the local music show DJs program their show based on the bands who are playing out in the upcoming week.
Be strategic in booking gigs, space them out. Your fans/friends will appreciate having some space between performances and will be more inclined to come to your show. The exception to this is if you are playing different markets, it's okay to play shows in Connecticut on Friday and Cambridge on Saturday. Buyers pay attention to this, if they see your band is playing TTs on Thursday followed by Radio on Saturday they will wonder what the heck is going on.
At the gig, be professional, don't be a prima donna, and be nice to ALL the staff at the venue. Folks that work at a venue talk to each other, if you are a colossal jerk to the sound guy/waitress/doorman/bartender they will tell the booking agent. Don't trash talk the talent buyer or venue while at the venue either. You never know who might be listening. Yes, I never booked a particular band ever again after several folks came up to me to let me know their lead singer was gripping about how the venue sucked, right before their performance at the "sucky venue", to his pals. Remember that there is no shortage of other musicians who would love to have the opportunity to play.
After the gig, follow-up with the booking agent to see when you can play again.