If you've never had voice lessons, but you can get some I'd take a couple. That way if you need help selecting a song, or with phrasing and style that will help. Plus you'll be more confident if you've worked on the song with someone.
Depending on the theatre you may not have to read or sing from the show, but just in case I would definitely listen to a copy of the cast album and read the script if a copy is available. Auditions are nerve racking enough without having to sing or read something you've never seen or heard before
That was my downfall at my first CT audition. I made the callbacks and had no idea what I was doing!
Break a leg!