Here is an interesting article from Global OUP ELT Blog.
You can find trailers on YouTube or sites like iTunes Movie Trailers. A typical trailer will be between 2 and 3 minutes long, although teaser trailers – those released sometime before the movie’s planned release – will be shorter, and typically give less of the plot away, aiming to create a general mood instead (these can be useful in their own right).
You should ensure you are not breaking any copyright laws in your use of movies in class and be aware of the suitability of the subject matter for the students you are teaching. Note that the majority of trailers will be suitable for class use, but ‘red band trailers’ are those which feature violence and/ or abusive language.
1) Pick a Movie
If you do show movies in your school, as part of a ‘movie club’ or similar, trailers can provide an excellent opportunity to decide what movies are shown, while encouraging students’ analytical and presentation skills!