Go to your bookstore and check in the film section. You're sure to find multiple movie guides there. Several prominent critics publish guides containing their reviews for many movies. Some even release a new guide every year.
Check out lists that have been made by film organizations. For example, the American Film Institute has many lists of great movies including top ten lists for every major movie genre.
For reviews of new releases, go online. There are plenty of movie review sites to choose from. Sites like Rotten Tomatoes display many reviews for each movie as well as an overall score based on the input of all the reviewers.
Find reviewers who publish regular columns. Once you find one who generally shares your taste in movies, you'll have a reliable guide to go by.
Use film festivals and awards ceremonies as a 'guide' of sorts. Usually, a movie has to do something right to win a major award. Everyone's familiar with the Academy Awards, but there many other film festivals that are held all over the world. Three of the most well known are the Sundance, Tribeca and Cannes film festivals.