Every designer knows that a fitting can set the tone for an upcoming project. The Costume Designer is like an ambassador. We are the first members to really interact with the actors besides the director. It is in the fitting that we mold the character and present it to the performer who will breath life into it. Preparing for a fitting could take weeks or just a few days, but the process and tools are always the same.
Design. Visual images are always helpful to communicate ideas. I like to have sketches, collages, and research present during fittings. This will help you keep focus on the clothing story. For my recent project Bad Boys Crazy Girls, I displayed boards with inspirational images of the character's growth from the beginning of the script to the character's resolve looks. This became a starting point of discussion between the actors and myself and set-up a formula for where the fitting would go.
Clothing. Of course you can not have a fitting with out clothing. Shopping, renting, pulling should have all happened before a fitting. The clothing should not be over crowded on a rack for ease of hanging and finding items. Remember that presentation makes a difference, for example, clothing should be hung on matching hangers and items should be steamed.
Tools. Well I've already mentioned that you will need racks, hangers, and a steamer. Also, to properly fit and prepare for alterations, a designer and their assistant should have safety pins (I prefer #3 sized silver pins), a tape measure, a ruler, note pad, pencil, hang tags, a camera, full length mirror, and possibly some lighting equipment.
Space. It is important to have the proper space. There needs to be privacy for the actor to change and enough space to step back and get a full length photo. Proper lighting is key to taking photos to look back at the work you did during the fitting and to see the items and colors you've brought to the fitting. Poor photos shown to a director could lead to a lot of unnecessary reshopping. It helps to make an actor comfortable with bottled water along with fruit or a snack to keep up the energy. Fittings can be along process and refueling and sugar help to keep an actor standing.
Finally, a good assistant can keep a fitting moving by passing safety pins, writing up shopping, pulling, and alteration notes, rehanging items. The designers job is to keep the actor engaged but the assistants job is to quietly record information and organize. All of these categories listed above will help a designer focus a fitting on character and story. Happy Fitting!!!