Watch movies -- a lot of them. Vow to watch at least one new film every day.
Find a community or source for your material. If there is an independent video rental store in your neighborhood, get to know the people who work there. Netflix also has an extensive library of films.
Watch every genre, from every decade. Watching all of Stanley Kubrick's films doesn't make you a film expert. Watch documentaries on Kubrick, find out who influenced him and who he influenced. And then watch documentaries on those filmmakers and find out who influenced them and so on.
Retain everything. There are millions of movies and you can't possibly watch all of them. But for each one you watch, try to be aware of what you like or dislike about it. You will eventually develop a sixth sense for the movies that you can avoid as you refine your tastes.
Write down your thoughts on films to help you concentrate on your analysis. Try to write reviews, even if they aren't being published. The more you write and think about film, the clearer your mind will become in relation to cinematic art.
Talk to people about films. Exchange ideas and observations regularly. If you can find a core group of people or a club with whom you may share your thoughts with, that will help you become a more credible expert on film.
Consider alternatives. There are schools devoted to film that would be beneficial. Another way to learn about film is by reading about it. Read biographies of famous directors and get as in-depth into their work as possible.