To begin with, it is necessary to clarify something very important: using films for teaching English is not a waste of time! Many teachers are reluctant to use these tools in their classrooms because they think that they waste a lot of time when watching a film. However, we must remind those teachers that they do not have to use an entire film to teach English, they can just use video clips from a film they have chosen and that is perfect both for teachers and for your students, because you use your time wisely and your students do not get bored easily when using short clips.
To follow with, the benefits of using films in the EFL classroom are as valuable as the benefits of using music in this instructional setting. First, students have the opportunity of having contact with English in a "real context". Although stories presented are mainly fictional, English is still used in the same way native speakers use it. Secondly, films can provide teachers with an attractive way of teaching new vocabulary!! If you present your students a video clip with subtitles, you can share new words with them, and work with those words in future activities. Thirdly, films promote students' motivation in the classroom! As teachers, we can do lots of activities based on the films they like, or that they feel identify with, and in that way they will be more willing to participate actively in the class.
Additionally, an extra-remark is needed here: subtitles in English can always be extremely useful to help students understand what the characters are talking about. Students usually have a hard time when trying to understand native speakers of English who speak fast, and usually in films native speakers DO speak very fast! In order to help your students to cope with this situation, add English subtitles to the video clips you will share, and they will not feel so lost.
In order to share a good example of a video clip that gathers all the benefits that have been previously presented, here you have an excerpt from the famous film "Catching Fire", the second film of the novel-based saga "The Hunger Games. If your students are teenagers and love this saga, they will totally enjoy doing an activity based on this video-clip: