Do your research. Rent the film and watch Liza Minnelli and Michael York perform. This will give you a sense of what the show looks like on stage. Pay attention to the choices the actors make, and decide whether you agree or disagree with them. Also, note that the role of Sally Bowles is American in the film version, while in the stage production she's British. You can also rent CDs of past performances. Listen to the songs and decide which one fits your voice best. Make sure you know the plot backwards and forwards.
Choose a song to sing at your audition. If you're auditioning for Sally Bowles, listen to her songs and decide which fits your vocal range the best. It's wise to stay away from the song "Maybe This Time"; it appears near the end of the show and requires a great deal of emotion. Pick a song you can easily perform at the drop of a hat. Rehearse by yourself or, ideally, with a musical accompanist. Work through the difficult sections of the song so you feel confident on the day of your audition.
Perfect your British dialect (Sally's dialect) for the audition. Go to the International Dialects of English Archive website (see "References") to hear various British dialects. If you're auditioning for the role of the Emcee, you'll need to perfect your German dialect. All dialects are available on this website. Listen to a few, then record yourself saying your lines. Replay it for yourself to track your progress.
Take dance lessons. "Cabaret" requires performers to be excellent singers, actors, and dancers. Research dance lessons in your area using the "dance-classes" site (see References section). Look for burlesque-themed classes; these will best prepare you for your audition. Attend a few classes, and inform your instructor of your intention to audition for "Cabaret." The instructor can help you refine your dance steps.
Rehearse your audition in front of a friend. Ask for her honest feedback. The more comfortable you are with your preparation, the smoother the audition will go. Ask your friend if there's anything you should change about your audition. Continue to fine-tune your performance until your audition day comes.
Get a good night's sleep before your audition. Avoid drinking alcohol, coffee and milk, which are detrimental to your voice. Instead, drink plenty of water and rest. Trust that you've prepared properly, and have fun in the audition. Casting directors love seeing actors who are having fun performing.