I want the part of veruca salt in my schools play willy wonka and the chocolate. How do I get the part?

Audition just like everyone else.

Practice the part at home, ask family and friends to give critiques to make you better. Then you audition and hope you get it. That's all you can do. If you're the best person for that part, you'll get it. If you don't get it, then do the very best job with the part you do get.