Find a venue and book it in advance. Ask fellow musicians about showcase venues that they have used before, and compare pricing, sound quality, seating capacity, location, parking convenience and the expected cover charge split when making your decision. Ultimately, you will want a room and stage where you can feel comfortable and where your guests will be comfortable, as well. If there is a minimum charge at the tables, be sure that your guests can order food or soft drinks to fill it, since many times industry executives may attend more than one show a night and do not wish to drink alcohol while on the job.
Find musicians, sound and lighting people (if the club does not provide them), and a musical director, if necessary. Be sure to budget rehearsals as well as performances when choosing who will work with you. Know how much money you can realistically afford to spend, and negotiate a fair price before rehearsals begin. Some musicians will agree to work for a "cut" of the door, but since industry showcases may pad the audience with non-paying guests, it is best to be sure you have enough money to pay your people before you perform.
Choose your material, clothing, backdrops or other related performance aids, and begin rehearsing as soon as you can. You probably will not need the full band for initial rehearsals, unless it is a band showcase. For a singer's showcase, a single pianist or guitarist may suffice for your first few rehearsals, and you can even tape your accompaniment so that you are able to go over the material at home. Be sure to provide all of your musicians with scores, charts or sheet music as soon as you decide on what you will be performing, and give them the opportunity to work at their own pace before showing up for paid rehearsals.
Create a mailing list of potential audience members and industry professionals. If you are a member of a professional performing association, such as American Guild of Musical Artists, American Guild of Variety Artists or other organizations, you may have access to pre-screened lists of people that have an interest in attending showcase events. You can pick up a copy of the "Ross Reports" at any bookstore, and find addresses of industry insiders that may be happy to audit your performance. Online social networking sites are another great way to build an audience. You can design an eye-catching flier, and post it on your profile page or email it to other members.
Create your set list, rehearse your material, check your wardrobe and discuss any last-minute lighting or technical changes with your tech people.
Be sure to arrive early on the evening of your performance, and let the front door people know of any industry people that are to be given priority or free seating at the door. Try to relax as much as possible before you go on, and when the lights go down, have fun above all else.