There are many things that go into Becoming a Film Critic, the highlights of which are below. They are completely arbitrary but they may help you in your film critic endeavors. They are as follows:
Be Prolific
The Ability to Write Quality Reviews
Watch Tons of Films, even Films you find Abhorrent
A Love for the Film Medium
Accessible Film Reviews
Following this link: What Makes a Great Film Critic?, you will find an explanation and discussion of all five points and a reading suggestion. It is up to you how you use this information.
