I have written a few technical books together with a co-author. From my experience "Side 1: Knowledge" is king. Before I explain a technical topic in writing I prepare every sample project beforehand. Complex sample projects are prepared in different versions (starting with the sample immediately after it has been created by an IDE, …) up to the final version. This has two benefits: I, as a writer, can offer the sample (step by step) for download to the readers so they can use them as a reference when something goes wrong - but more importantly: It helps to structure the writing process because I know the steps I have to describe. I know when something essential has happened (because I have created an additional version of the sample).

A rough outline created in advance also helps.

I am also talking to myself - a lot. Before writing something down for my book I explain it to myself.