Qualifications
Almost every successful dancer has had a ton of training. Many start in local studios when they're just kids. If you want to go beyond looking cute in your tutu for Great-Aunt Linda, you'll eventually need to sign up with a legit professional training studio.
Choosing the right studio can be a big decision. Some are awesome, and some aren't so great. Learning your moves with the wrong teacher can really set you back. Dancing is all about muscle memory, and bad habits are very hard to break.
Getting into the right college program can also be a big help. Programs like the one at Julliard or NYU Tisch can give you a huge leg up professionally. There are many other universities with great dance programs; do your research and find out which one is the best for the style of dance you want to master (source).
Getting a regular college degree is also a good thing to have in case you need a backup plan (source). If an injury takes you out of the business early, you don't want to be that thirty-year-old in undergrad.