I think an extremely big thing at an audition is simply saying "Thank you" at the end. It makes you look professional and courteous, without being too much of a kiss ass.
And if you don't have the karaoke or the sheet music - sing it a cappella. Don't sing along with the CD. Please, dear God, please.
Songs NOT to audition with: On My Own, Tommorrow, Maybe, Defying Gravity (unless you know you can hit those notes ANY day of the week), Don't Cry For Me Argentina, or All That Jazz. And, Popular - unless you're auditioning for Adelaide in Guys & Dolls and you want a character piece. *nod*
I definitely agree with whoever said to audition for the age of the part. If you're looking to play Miss Hannigan in Annie - singing 'Castle on a Cloud' might not be the BEST choice. :]
"The tick BOOM tick BOOM is so loud I can't hear the rain on the grass. I can't hear the wind. I'm about to scream. But I realize I'm not alone."