Music ^__^

Music is a key factor as it helps the mood and the tone of the trailer itself! Usually the music used in the trailer isn't from the film itself, the film score(background music) may not have been produced yet even. The music used in the trailer may be, Music from the score of other movies,
Tarantino does this a lot, as he used a wide assortment's of songs taken from various artists such as "Miserlou" and "surf rider". Music can also be popular music, chosen specifically for its tone.