Do you enjoy watching movies? Have a definite point of view about them? If you like watching movies every day and analysing them from a viewer's pleasurable point of view as well as from a filmmaking standpoint you might be a good movie critic. Movie critics are sought after to provide the general public with sneak peek opinions of upcoming movies and new premieres.
Watch movies. Watch lots and lots of movies. Get to know every actor, actress, director, writer, cinematographer and producer. Create notebooks or spreadsheet with notes on their particular styles, people they work with or work in general. Does a director make all of his work from a particular standpoint that is completely obvious to all who watch?
Learn about the filmmaking process from writing and development to post production editing and marketing. The more you know the better you'll be able to understand where and why movies fail or succeed and you'll be able to include these points in your reviews and articles.
Read other movie critics reviews in the newspaper and online. Figure out whose style you like and why. What about it is inviting, enticing and entertaining? As a critic you will develop your own style and that might depend upon who you're writing for as far as what they will want to read. A middle America paper won't go for the same sarcasm as an East Coast gazette.
Write some sample movie reviews. Try writing them in different styles and perhaps even in different formats if you can think of a better way to do it. Contact your local papers and send them your samples. Ask if you can write a weekly column or review. If they don't jump at your offer don't give up. You can always start writing online. There are tons of sites looking for movie reviews. Many of these sites don't pay but it can be a start, get you some clippings and be something to put on your resume. Wherever you write for make sure to save each review your write. If you receive commentary or criticism of your reviews save that as well, you may be able to use it later.
Continue to apply to papers and online to get more and more exposure and experience. If you have a website start a blog and write reviews. The growth of the Internet can be a great place for your to be seen and heard. Start a website if you start to get a following and post your reviews there. Pretty soon you'll have advertisers contacting you to put up advertising and paying you for it. Be persistant and you will get more and more jobs and eventually higher paying work.
Study filmmaking. Study film history. Get to know actors, directors, writers and others by name. Look for emerging new talents.
Don't criticise a film just because you don't happen to like someone in it or affiliated with it.