For WUHS Musicals or Musicals With A List of Songs:
Look over the songs and again, consider your voice part. Pick a song that is within your range whenever possible.
If you have a voice teacher, they are a good resource for choosing a good audition song. Ask them what they think!
Pick a song that is within your acting range as well. Play to your strengths.
Consider which songs fit your desired character best. If they're a very happy-go-lucky character, there likely is an audition song that reflects that sort of character!
Again, take your interests into account. If you don’t like the song, you likely will avoid learning it.
Begin learning as soon as possible. A prepared audition is better than an unprepared one.
For Open-Pick Auditions:
Look for a song that fits your voice type and character. Musical theatre is generally best, but usually not 100% required. Double check the audition requirements and soundtrack for the show to make sure that you pick the right genre.
Again, voice teachers are a good resource.
Try not to pick a song that is “overdone” (ex. “Defying Gravity”, “Popular”, “Memory”, “I Dreamed A Dream”); again, this is best but not required. If you can perform a song exceptionally and it's a popular song, go for it! However, be aware that you must perform it really well if you are going to do a very popular piece.
Play to your strengths.
Consider your interests.
Begin learning as soon as possible.