What makes a good film trailer?

Don't give too much away
One of the problems film directors have when making trailers, is to not give too much away of the plot. While attracting the audience, it is important not to give too much away otherwise it would damage the viewers enjoyment when watching the film.

Don't be too cryptic
A complete opposition to my first point, yet it is also important that some information is given to the audience. Such as the genre, who stars and the director or the movie. If the Director is not well known, it is important that the trailer attracts the audience. Otherwise they may think it is a disappointment.

Speaking to the target audience
In a good movie trailer, they must put in the correct amount of information to attract the target audience. The correct language must be shown to the target audience. an example is a teenager talking slang- this would attract more of the younger generation as some talk the same way.  Sometimes, a voice over is used to talk to the audience to briefly explain a situation. This can also indicate the genre of the film too- as the voice over could be funny, or dramatic and mysterious.

Effects
The effects used must match the mood of the trailer. A faster transition helps to set a more intense mood for a horror or thriller, whereas a slower one can give a more comical or dramatic feeling. Music can also be used to explain the mood and genre. For example a more Indie/bangle type of music and be used to show the film is from Bollywood.