A document is only as good as its worst channel of delivery. Here is one memo about to go to two hundred people. Run it through four channels — your eyes, a screen reader, a greyscale printer, a phone — and toggle the fixes until every check on the rubric passes. Watch the first channel closely: it is the one context in which the document is guaranteed to look fine.
The channel
The same file, delivered four ways. Nothing about the memo changes when you switch.
The fixes
Each one is small. Each one improves the document for everybody, not only for the reader it was aimed at.
Aa—contrast ratio
Light grey text on white is the most common design mistake in professional documents. Guidance sets 4.5 to 1 for ordinary text and 3 to 1 for large text (at least 18 point, or 14 point bold); the enhanced level asks 7 to 1 and 4.5 to 1. You do not have to guess — the number is computable, and this slider computes it.