Firstly research the current critics, read a few reviews see what flies as passable. Then start writing reviews and submitting them to fanzines and newspapers. If they're good enough you may get a freelance pay or a permanent spot on the writing staff.
Start small and write movie reviews for a local alternative newspaper. Once you have some clips, you can shop around for opportunities in bigger publications.
First off, you have to have a journalism or perhaps even a theatre background. If you do, then you simply apply to be a writer to a specific newspaper or theater critic forum.
First, major in theater arts in college. Immerse yourself in the theater life, learning all aspects of what it takes to make great theater. Slowly you will make a name for yourself and begin to work as a critic.
