What is "stage presence"? It's a quality sometimes called charisma, charm, or magnetism. It's that "it" factor or "X" factor that makes you compelling to an audience. It's not necessarily physical beauty, although attractiveness can certainly be a factor.
At least 50% of an audition begins when you walk into the room. Having an inner self-confidence - not to be confused with arrogance - goes a long way toward making the auditors receptive to what you're about to offer. And that's even before you've had a chance to say "hello." The casting people need to believe that you have something of value to offer their audiences.
Often, I've found that the people holding the auditions aren't sure themselves about exactly what they're looking for. But don't try to be something you're not. I find that a performer's "essence" will come through regardless of what is said, worn, or sung. If the casting notice is asking for a "quirky, cute, and funny" character, and that's not who you are, it's almost impossible to fake it.
You're there to sell a product, and that product is YOU. If you don't believe you're good, it will be apparent to everyone watching. The audition is YOUR party; think of the observers as your guests. Leave your problems, the weather, distractions, and The Waiting Room outside. You need to appear to enjoy what you do, and that you're having a great time. It amazes me how many performers look like they're going to the dentist when entering the audition room!
Stand up straight, look the auditors in the eye when speaking, and put on a good show. I'm not minimizing the nerves that everyone feels when being assessed, but you need to put those feelings aside as much as possible. In the words of Oscar Hammerstein II:
Make believe you're brave
And the trick will take you far.
You may be as brave
As you make believe you are.
One important way to feel more comfortable when auditioning is to be prepared for anything! Have extra pictures and resumes even if you believe they have one already. And prepare a backup song or two in case you're asked. Also, bring your dance clothes even if you've been told there will be no dancing that day. Remember, "Failing to prepare is preparing to fail."