[wavegeek]

I like his point about lack of ambiguity. Nothing makes me want to punch an author in the head (without, to be clear, any possibility I would actually do it) like lazily creating an ambiguous notation, which is supposed to be "clear from context", but rarely is. As for example the Einstein summation convention which is to be ignored "when clear from context".

I would add

1. Clearly telegraphing notations. Not hiding them in the middle of long paragraphs or even, and yes I have seen this a few times, defining essential notation in an optional exercise.

2. Having a glossary of notations, so people don't have to remember every single notation and to read every word of the book sequentially.

3. Not creating low value notations that may be used only once and then, possibly forgotten. I have read books with > 1 new notation or definition per page, mostly forgotten thereafter but some random subset needed later, and you are not to know which.