One of the best-kept secrets about the magic of theater is how actors and actresses can change elaborate costumes in seconds. When an actor changes from one costume to another and only has a very short amount of time in which to do it, it is called a "quick change." For privacy, quick changes are usually performed in a special booth, but actors are generally provided with one or two dressers who can help make the quick change happen as flawlessly as possible.
Designate an out-of-the-way corner or quick-change booth ahead of time. Be sure your dressers know where to meet you and what items you will need. Always be sure to check your quick-change items yourself. If your dresser is setting your costume for you and forgets something, you will still take the blame, even in professional theater.
Be sure that everyone in the cast and crew knows where and when your quick change will be taking place. Because there is no time to run to a dressing room, quick changes are always done as close to the stage as possible. This means you may be in the way of foot traffic or set pieces while you are changing. Always speak with the stage manager before coordinating a quick change on your own.
Practice before the show. It can be tedious, but practicing taking off costume #1 and putting on costume #2 can save embarrassment in the long run. Have yourself timed, and be sure your dressers are helping rather than hindering the change.
Be creative. Any shortcuts you can use will save you time and energy. For example, if you're only in the first costume for a few minutes and your back never faces the audience, consider undoing the zipper a few inches down your back to save time. This way, you can reach the zipper and undo it as you run to the quick-change booth. If you're having trouble making the change, ask the director and costume designer if you can cut down on props and accessories to make the change easier. Usually, a director will be very understanding, as she wants the show to run as smoothly as possible.
Leave the stage as gracefully and calmly as possible. You do not want the audience to catch a glimpse of you racing into the wings to change your costume.
Before you're about to make your entrance in costume #2, be sure you or your dressers have moved costume #1 out of the way--and, if there's time, prepped it for the next performance. If the costume lies on the floor for the remainder of the show, it could get lost or ruined.
Always double-check that all of your props and costumes are in place before the show starts. If you're late for a quick change, find the best possible time to enter the stage and try to help the other actors get the scene back on track.
Be careful when running and fastening pins in the dark. If you're in a rush, you're even more likely to hurt yourself.