Agree upon a working date with your band, and everybody else involved with the show. Try to schedule the show on a weekend evening so as many people will be able to attend as possible. Some clubs, and other performance venues will only have weeknights or afternoons available, as they have scheduled regular acts on the weekends. If this is the case, go for the weeknight. You will be hard pressed to find an audience during the day.
Secure a venue. Scout local performance venues in person to gauge the stage space, and access to the stage. If your act requires a large band, make sure the musicians will have enough room to play. Be sure the dressing room is adequate and whatever other requirements you need are covered. If you check out a venue solely online, you will not be able to tell if the space is adequate.
Hire a sound technician. Most venues offer packages that include sound and light technicians, but many times they are inexperienced. You can usually get away with minimal light changes, but it is imperative that you have an excellent sound person. All of your rehearsing will be for nothing if you cannot be heard, or the sound is not enhancing your voice or instrument as it should. Poor sound can be disastrous. The pitch can be affected, you can be drowned out, or muffled, and many other equally awful scenarios. Don't risk it. Go to see other shows, and then spend money on a sound person whose work you love.
Arrange a rehearsal time, and run through the act with full everything; lights, sound, costume changes, everything. If your musicians are union players, you will save yourself money by scheduling the rehearsal a few hours before the actual show. You will be exhausted by the end of the night, but you will not have to pay for another day. It is cheaper to rehearse, then give the band a food break and do the gig all in the same day.
Hire a reputable video production company to film the show with multiple cameras. There may be agencies that are out of town or state that you want to send promotional materials too, and a DVD will be your calling card. You will have to hire an editor to create a professional quality DVD of your best five to seven minutes, and perhaps another video of the entire show, should an agent require it.
Send out massive emails, and letters announcing your showcase to agents and producers. You will find addresses in the "Ross Reports," but most of the agencies that book acts for cruise lines and resort communities are located in Florida. Also send invitations to everyone you know to fill the audience. You will want your family and friends to be yelling at the top of their lungs in support of you and giving you a standing ovation at the end. Include this info requesting the ovation and great audience reactions in your emails to friends.
Send your DVD, headshot (and 8 by 10 inch photo of you), resume and a one-page bio in an attractive folder or notebook to the agencies that were not in attendance the night of your show. See Resources for agency listings. Wait two weeks for a response and then send a friendly email to ensure that the companies received your package.