Interview the hirer and ask what the scope of the project is. Find out if all of the research and outline has been done and if not, who will be doing it. Ask whether the hirer intends to collaborate on the actual writing or prefers to allow you to do the work and give his approval.
Set a schedule for when each phase of the project must be done so that you understand the time frame and how much of your other work you may need to put on hold. Set milestones, each worth a percentage of the total price of the contract, so that you will get paid as you go along.
Agree to a percentage up front, another percentage upon completion of the research and outline, if any, another percentage upon completion of any agreed upon amount of the first draft and the remainder upon completion of the first draft. Agree upon any residual, or royalty percentage you will get upon publication of the work.
Calculate how long similar projects typically take for you to complete by comparing it to work you have done. If you are new to writing, plan on being able to write five to 10 pages a day working eight hour days, including revising as you go.
Determine how much you want to make per hour. Add up the number of hours it should reasonably take to achieve the desired page count and multiply it by your hourly rate. Add 10 to 15 percent for extra time not accounted for, so you won't feel the need to increase your price or feel taken advantage of if it becomes a little more work.
Divide the amount into the agreed upon percentages and write a description of the work you intend to do, the time frame and the amounts that will be due for each milestone. Have the hirer sign this agreement, collect pay for the first portion and start writing.