Found a good tip for preparing for auditions that require you to perform more than one monologue:

In between your monologues, you need to make a physical and mental transition. Use your transition to show what a smooth and crafty actor you are! Do something with it. For those of you with long hair, you might want to remove a clip and change your look for your second piece. For those of you with a grungy 2nd character, you might want to kick off your shoes in your transition. Use your imagination! Without making a complete costume change, how can you change your look? Rehearse your transitions from introduction to character and in and out of characters ahead of time. Don't say things in the middle. Run the whole thing through as a production, not as several productions broken up with intermissions.