Determine the parameters of your fictional world. Use a legal pad and pencil to write out the powers and weaknesses of the zombies, the weapons which will be effective against the zombies and the powers that the heroes will possess in the book. Be creative, but use some established zombie "truths," such as the idea that zombies can be killed only by decapitation or fire and the desire for the zombies to kill the living.
Write out character sketches and a basic timeline for your book. Determine the motivations and desires of your main characters, and choose which ones will become infected and which will be "ultimate survivors" who triumph over the zombies at the end of the book. Sketch out a progression of how the zombies will cut off survivors from help and how quickly society will collapse. Remember that small rural areas will have fewer resources and that urban areas with high population densities will become overrun quickly.
Determine the cause of the zombie infestation. If you choose to have the infestation created by plague or medical malfeasance, research any medical terms and treatments needed for the book. Accurate medical information can be found at local college libraries, which should have medical texts available. If research is done on the Internet, ensure that you are using a reliable source for information.
Write every day. Set a timer to ensure that you write for the full amount of time and keep track of your word count. Set goals for both time spent writing and words written each day to stay on track for finishing your zombie novel. Word calculators can be found on the Internet, and most word processing programs include a word-count function. Use the spell checkers and grammar checkers available on most word processing software to ensure that your work meets spelling and grammar standards.
Submit your book to literary agencies or publish your novel through a self-publishing company which sells books on Amazon.com and other online retailers. Finding an agent is the first step to being published by a large retail publisher. Send samples or a manuscript of your work to the agent as well as a clear and concise letter of introduction and information about your novel, including the character sketches you wrote and information about the research you have completed.