Draft a structure for your documents at an early stage. Don’t start writing “intuitively” and let the documentation “evolve.” If you start writing without having a plan for the structure, the whole process will take longer and will be more expensive.
When working on a plan, revising a decision costs nothing: All you have to do is to change your mind. Later, however, when you’re working on the actual document, revising a decision will be costly. You will then have to change everything that you’ve produced so far. The more you’ve written, the more the changes cost in terms of time and money.