As Alfred Hitchcock used suspense effectively within his film , I aim to use this technique- also drawing on the elements of mistaken identity that he uses in a number of his films.
A normal teen girl who loses her best friend (to murder) becomes so distraught see begins attending therapy lessons. This leads to her meeting a boy (the killer) while trying to figure out the who the murderer is. (Murderer has obsession with hair -all victims has long hair).
Cutaway - could use to interrupt the continuity of action ,for example = showing the murder ,cutting to the evidence from the crime scene and cutting back to the final shots of victim before (she) dies.
fast cutting - speed up specific point of actions nearing the end of the trailer.
L cut (with sound) - conversation between main character and therapist about friends death cuts to shots of the murder.
smash cut –as the main character is being pursue- when something bad is about to happen to her.
slow motion - can slow down struggle between the victim and the killer (close up of victims face and can only see gloved hands and arms of killer).
Create fog/smoke -adds to the thriller element and echoes the technique used by Tim Burton in Sleepy Hollow
diagetic sound - the music can start low (maybe use string instrumentals) , begin to take on a darker sound to correspond to the shots and at the end could use the cinematic drum sound, used nearing the end of many Hollywood trailers.
non diagetic sound (voice over, etc.)- Voice over (voices of characters from part of the film with shots corresponding to the speech (which is one of the conventions of a trailer)