Tally and Garage Band

I'm creating our sound track on garage band. When doing this task I need to take in to consideration certain codes and conventions, of a thriller soundtrack, such as creating an atmosphere that fits in with the images on screen. Also I need to raise the volume at climaxes and create a sort of spooky music, to fit with our setting. I Liked the soundtrack in SURFACE, which it works well to appeal to its target audience. I also need to take in to consideration non diegetic and diegetic.