First of all, you need to get a film guide which is easily available on almost all book stores. You will see that these film guides provide information about the latest and upcoming movies including the details of the movies.
You should just go through the summaries, commentaries, previews and reviews of these movies and select a few ones that you think are most interesting for you. You should also pay attention to the acting quality, visual beauty, screen play and also how much depth a movie is providing.
You need to watch as much movies as possible which will help you in developing an in-depth understanding of the summaries, plot and overall depth of the movies.
Make sure you do not make yourself limited to a specific genre as it will also limit your understanding and you will not become a good movie buff.
Watching different types of movies help in increasing a general understanding and you will be able to enjoy different genres equally because you will be able to analyse everything in an accurate manner.
If possible, try to watch older movies and also foreign movies which will help you in developing a greater level of understanding and you will become a good movie buff.
If you feel any confusion or fail to understand any particular aspect of a movie, then you should watch it again and again until you leave your seat with a clear mind. It will help you to understand even the complex situation presented in a movie.
You should also do online search for checking reviews and commentaries of movies which will help you to understand all aspects of movies in a better way.
You can visit the website of IMDB, a leading movie database, where you will be able to check the overall popularity of a particular movie.