Set a word-count goal. Goals can be weekly or daily. Novels are generally a minimum of 50,000 words, although an average length is between 80,000 and 100,000 words. If you plan to write a novel-length book and complete revisions in 90 days, divide 50,000 by 60 for a daily word goal or divide by 8 for a weekly word goal. These goals will ensure you reach the minimum 50,000 words for a novel in 60 days. The remaining 30 days can be devoted to edits and revisions.
Write down any book details you have and ideas for characters. If you are doing a proposal for a nonfiction book, an outline will be required as part of the proposal. Outline each chapter of the book, jotting down notes for each chapter. If writing a novel, write down plot ideas, character traits, settings and any snippets of dialog you have. If you know how you want the book to end, include this information as well. If for your nonfiction work you will need to interview people, make a list of these people and include their contact information.
Write the book. You do not have to start at the beginning. If there are other portions of the book you are drawn to write about, write those portions first. Keep edits while writing to a minimum--you can edit after you have your first draft written. If you are writing one chapter but have an idea for another chapter, stop writing, quickly write the idea down, then return to your current writing. Avoid re-reading what you have written. The objective is to get a first draft down on paper and constantly reading what you have already written is reviewing, not writing.
Let the completed first draft sit for at least two days. After two days, start editing and revising as needed. If you know a good editor, have that person read and edit the book for you. You should give the manuscript at least three thorough editing passes and at least one straight read-through. If you have others who are willing to help, have them read it as well.