•you need a good story.
•have the story told from the point of view of the person with the most to lose.
•try and have multiple points of view, as this allows the audience inside multiple characters heads.
•immediately open your thriller with an action theme, then include the character information later.
• make it clear early on what the protagonist wants, and what he fears.
•the main characters have to change emotionally thoughout the film.
According to justicemitchell.com (http://justicemitchell.com/justice-mitchell/2010/8/23/horrorthriller-movies-the-key-ingredients-to-fear.html) they believe the essential ingredients of a thriller are:
• make an everyday task frightening.
•try and make a scene scary in the day.
•try and make a scene thrilling without a musical build up.