Consider your strengths and weaknesses. A goal is not realistic if it is not achievable. Although you may want to set product goals that are highly ambitious, they will be nothing more than pipe dreams if you can't achieve them. Take some time to consider how fast a writer you are, how experienced you are with the project at hand, how well you know the material and how much research you will have to do. Think about how much you can comfortably write in one sitting, and how many sittings you can comfortably fit into one day. Also take into account your work and personal calendars. Product goals for writing can easily be sidelined by a busy month of events. Once you have a good grasp on this information, keep it in mind as your proceed.
Set a goal date for the first draft. This is where some of your earlier calculations come in. How much of the product can you write per day? Divide that by a rough estimate of the finished product, add in days off, weekends and special occasions, and you will arrive at the number of days it will take you to complete a draft of this project. For example, if you can write one page per day, and your product is 30 pages, you would start with 30 days, add in eight days for weekends and two personal days for events, and set your draft goal at 40 days.
Break your project into manageable steps and set goals for each step. Larger goals are great, but you need small, actionable steps to get you to the finish on time. Within your span of time, find ways to break up the project into smaller parts. If you are writing a manual, perhaps week one will be the introduction, quick reference, warnings and parts diagram. Breaking this down further, you can set Monday as the day you do the introduction, Tuesday and Wednesday for the quick reference, Thursday for warnings and Friday for parts diagram. Map out your entire project, leaving room for catch up days and unforeseen obstacles.
Review your draft and set a revision date. Once you have completed the draft, use the same method to set a revision date. If you know you can comfortably edit 10 pages per day, and your project is 100 pages, give yourself 10 days plus two weekend days, and consider adding in an extra day or two as a safety net. Mark this day on your calender, and begin breaking the product into editing tasks.
Break the piece up into manageable editing chunks. Set an agenda for each day that specifically includes the day's editing tasks. Write which sections or chapters are to be edited and stick to your schedule. If you can, give yourself time to let the project sit for a few days once you think it is done so you can approach it one last time with a fresh pair of eyes.