Suspense is a difficult thing to do right. It's not like a movie where you have the luxury of music that can be used to influence a viewers emotional response. I would say that it is something that has to be carefully crafted and slowly built up over a number of pages at least. A good device I find that some authors use is to shroud the menace/evil so that the protagonist spends a good period of time unsure about what it is that is chasing them or even completely unaware of the danger.
Suspense is relieved by revelation. Therefore, delay revelation as long as possible, and only reveal the minimum necessary for the story.
