Read a variety of different espionage novels and note what you feel was effective, and what you did not enjoy. Pay close attention not only to the plot and story, but also to the writing style, as this will help you later as you work on finding your own voice.
Brainstorm freely on your espionage story. Allow yourself to write ideas on characters, setting and plot twists freely without worrying about editing or even being logical. Remember you have full creative license in your writing. Espionage tales are often woven with other genres like fantasy, sci-fi and horror.
Research and save articles and information that will help you as you build your story. Consider, for example, the city or town where your espionage novel unfolds, and research that location. A spy novel will almost always feature futuristic gadgets for spying and a higher than usual level of technology, so research in that area is also beneficial.
Write a short biography for your main character or characters. Frequently, espionage novels focus too heavily on plot and the characters fall flat, leaving readers unsatisfied. Develop your characters first in order to make them more lifelike and real.
Devise a plot outline for your story. By nature, a tale of espionage is full of lies and secrets, so you must be particularly careful in avoiding plot holes and inconsistencies. Stay organized using index cards or a spreadsheet to keep track of story lines, especially if your story will have several different character points of view.
Write your story scene by scene, referencing your outline frequently. Keep the tension in your story high—a key element of an espionage novel—by constantly putting your main character in dangerous situations and continually raising the stakes or consequences if he fails.
Break for a few days or weeks away from your book once you finish. Then return for a read through and revision. As you read, take note of both line edit details such as punctuation errors, as well as larger, plot-related issues. Ask yourself in every scene if the scene is necessary to the story, and whether tension and action—vital to a good spy tale—are constantly present.