Create an outline for your technical book. Before starting the writing process, you need to determine what your readers will want to know about the topic and also what they should know. Decide if your book will be a reference book or learning book because successful books have a focus.
Set a daily goal to write so many pages a day. Books take time to write, so if you don't work on it every day, it will never get done in a reasonable time.
Research your topic thoroughly by speaking to experts and reading material on the web and from other published sources. Some of your readers will require background on the product or technology you are writing on.
Set writing conventions. For example, are you going to use Associate Press (AP) style or Modern Language Association (MLA) style? Whichever you prefer or choose, you will need to read their stylebook so you know if contractions are allowed, how much punctuation to use and what needs to be capitalized.The style guide you choose will also explain how your references should be listed and cited in the text.
Draw out or create diagrams on the computer to help explain your writing. Use software that you're comfortable with such as Adobe InDesign or Visio, but make sure you can convert the figures to TIFF or JPEG in case your publisher prefers one type over the other.
Draft your technical book and read it three to five times before having others review it. Getting feedback from people who are completely unfamiliar to the topic can give you the most valuable pieces of criticism.