How can I not have my music sound like Hilary Duff and musicians like Aly&AJ?

You should make sure your vocals aren't very light. Put lots of emotion into your music. If your song is sad, sound sad(but not whiny), if your song is angry, sing louder in some points. Good Luck, and p.s. when you make a cd, email it to me at jgomez60@charter.net