Here's an unusual suggestion...
In the 1980s the children's publisher Usborne published computing books for young readers and a few years ago they made the books available for free download. The books use illustrations extensively to explain concepts. Not only are these books well written with clear, concise explanations, they are also more readable and enjoyable than many programming and computing books published for adults today.
Anyone writing a technical guide (of any kind) would benefit from reading these as a source of ideas and inspiration: