I just learned about a great toolkit for writers, especially those writing for people (patients) with potentially low literacy skills. However, it seems to me that all of these principles would apply to technical writing across the board.
The free download (PDF) is the Toolkit for Making Written Material Clear and Effective, offered by CMS, the Centers for Medicare and Medicaid Services. Their audience is those who create “written material intended for use by people eligible for or enrolled in Medicare, Medicaid, or the Children’s Health Insurance Program.” Here are the topics you’ll learn about:
Try it! You’ve already paid for this valuable educational experience with your taxes.