There are lots of things to think about as you prepare for an audition besides your song (if you are even auditioning for a musical). Some directors may want a head shot or resume. While I'm not sure it sways my casting decision, it is impressive and makes you stand out if you have those. You do want to be memorable - in a good way.
Dress appropriately. That doesn't mean you need to come in costume, but do understand that at an audition you are very specifically saying "Judge me!" What does your clothing say about your level of commitment, your desire to become part of the team? If it says, "I don't really care much about this," you had better have a lot of talent to overcome your first impression! What you wear can make you blend in or stand out (in a good or not so good way!). It's not huge, but it can be a factor when you're trying to impress people who do not know you.
Wear shoes you can dance in. I am convinced I was cast as a dancer many years ago simply because I brought my tap shoes to the audition. Maybe you'll be asked to dance, maybe not, but it is a reasonable expectation (at a musical audition), so don't come looking like you had no idea that a potential performer might be asked to perform.
Bring something to write with, just like a job interview. You will be asked to fill out a form. Be prepared, boy scout! You will probably be asked for some sort of list of past experiences. If you don't want to try to remember everything on the spot, write it down ahead of time and bring that with you, too, just like a job interview …
Try to be calm - difficult, I know. Stand in front of a mirror and practice saying, “Hello, my name is …. and I’ll be singing …. from …” until it feels natural and you look like you’re speaking with confidence. One of the best ways to overcome audition anxiety is to do it a lot. Audition for lots of things. The experience is valuable and you might find some great opportunities you didn’t know were even there.