Focusing on the task at hand is of prime importance when waiting for your audition. Use the time in the waiting room preparing for your audition, rehearsing lines and mapping out the emotions of the script. Be aware that you are being judged not only on your performance in the audition room, but also on your behavior in the waiting room. An actor trying to psyche out their competition could see their actions backfire, if vigilant receptionists and casting assistants report this behavior to the casting director. Avoid gossip and chatter---guard your reputation well.
Upon entering the audition room, recognize each and every person in the room, but remain professional. No matter how famous a director, actor or producer you are auditioning for is, remember to focus on the task at hand. Don't comment on their work or fawn over their talent. You want to be viewed as an equal, so act like an equal.
Being confident about your own acting ability and what you can bring to the role is probably the single most important trait you can have. In a twist on a quote (often attributed to George Burns) that "Acting is all about honesty. If you can fake that, you've got it made," an actor should be aware that "confidence" is much more important than "honesty." And faking confidence, which seems to be an oxymoron, really isn't. Unless you're literally shaking in your boots, no one need know how nervous you are; control your fear and project calm. Confidence is infectious. We all want to be around people who are confident, so make yourself the one everyone wants to be around.
Tactfully parry questions of age by stating a range of ages or roles you can perform instead of revealing your real age.