Paint a vivid picture of the scene. You must tap into every sense to do this. Describe what the character smells, sees, hears and feels. All of these senses should be used subtly to create a sense of dread. To create suspense a reader must feel as though they are in the scene with the character. Make sure that you craft the scene accordingly by being descriptive.
Know that as the scene develops, you will start to hit your storyteller mode. The words will flow as you think your way through your horror scene. The natural tendency for any writer is to be predictable because you are flowing with the first thoughts that come into your mind. It is almost a form of free writing at this point. Roll with the scene and continue to the end with your train of thought. Finish the scene in this way.
Review the scene with a critical eye. As you read through, keep your eyes open to any predictable passages. When you find yourself feeling as though a scene is overly predictable, then it is. Go back in and find a new way to reach the same end. Little things can go a long way in a horror novel to keep it fresh. You do not want to write a book where everybody feels they have seen it somewhere before.
Make certain that you do not solve every problem during the course of one chapter. A horror novel should build suspense up to a climactic ending, rather than be a series of miniature problems being solved as you go. This is the most common mistake in horror novels. Leave every chapter as a cliffhanger that the character can not overcome. In the next chapter let them survive just enough to receive a new bigger problem. A brilliant protagonist that easily overcomes every problem is a recipe for a boring horror novel to be sure. Make them suffer.
Give the final scene of your horror novel a dramatic explosion. Make certain that the buildup was worth the wait for the reader. They are investing a lot of time in reading your horror novel, and they should get the goods. Deliver an ending that will leave them shaking with explosive action and unpredictable answers. Leave the opening for a continuation of the story. The perfect horror novel leaves the reader gasping for more.