Read over your plot outline. Make sure that it is interesting rather than commonplace and mundane. Tweak your plot and characters, if necessary, to make them mysterious and intriguing. Unreliable or deceptive characters can add an aura of mystery to your narrative.
Write a catchy introduction to get your readers hooked from the beginning. For example, start the narrative "en medias res" -- in the middle of things -- in order to leave your readers wanting more after just the first few pages.
Create a sense of impending doom in your novel or short story. A happy, pleasant work is rarely a page turner. Put your characters into strange or surreal situations. The easiest way to create suspense in a narrative is to place the main character in a situation of impending doom.
Vary the pace of the novel or short story. Rather than having the work plod along at a steady pace, speed up the narrative as the suspense increases. Then slow down the pace with a cliffhanger designed to make readers read the story in a state of panic. This method will leave readers wanting to know what will happen next.
Put the main character through a variety of "close shaves" or "near misses." This reminds readers that the main character is in imminent danger and also prevents them from becoming bored with the narrative.
Write an open-ended conclusion to the novel or short story. You don't have to wrap everything up neatly and solve all of your characters' problems at the end of the work. Keep readers in a state of suspense and wonder long after the narrative ends by answering only some of their questions.