At the heart of any valuable suspense narrative is an inherently good protagonist whose greatness is only matched by the intrinsic evil of the antagonist villain. Both hero and villain must be curious, layered and painfully human. The more capable you make these characters, the more engaging they’ll be, and the more your reader will be forced to wonder what these characters are going to do next.
Establish what’s at stake, clearly and as early as possible. If your hero works in an office and must prove she’s worthy of her job, let the reader know the financial, social and personal ramifications for what’s at stake. This will heighten the tension, plant an element of uncertainty, and lay the foundation for a strong feeling of suspense. The higher the stakes are, the greater the suspense can be.
Nothing heightens tension and suspense like an established, narrow time restraint. Not only does your hero have to prove she’s worthy of her job at the office, but she’s only got three days to do it. A ticking clock creates a heightened sense of urgency, and demands that your hero to perform under pressure. This element draws your reader closer to the action, and invests him deeper into what’s at stake and why.
Throw difficult, harrowing problems, issues and situations at your characters. Keeping your reader guessing is at the heart of the uncertainty on which suspense is based. Also, a reader will measure the greatness of your hero by her ability to overcome obstacles. This means that the greater your villain is, the greater is the potential for a truly brave and strong hero. Force your villain to prove her value by highlighting the problems she overcomes. It will make the final showdown between villain and hero -- the most difficult problem -- that much more tension-filled.