Blake, Gary, & Robert W. Bly. The Elements of Technical Writing. New York: McMillan, 1993.
I read many technical documents and wrote a few. Most could be better.
I admit it can be difficult to write documents that are correct and detailed that are also succinct and clear. Blake and Bly offer a lot of advice on good technical writing. Their pointers are applicable to reports, articles, manuals, specifications and proposals.
In addition to providing instruction on technical writing, the book is also a reference. Technical writers or the technical professionals who are writing could use it as a stylebook. Since it focuses on technical writing, it is shorter than most general stylebooks.
The Elements of Technical Writing is a model of good technical writing. The authors use of the principles they espouse. In particular, the book is very well organized. Readers who are seeking direction on a particular issue will be able to quickly find it by referring to the table of contents, the index or even a quick flip through the chapters.
Technology changes, so the chapter on software writing aids is probably outdated. However, the principles of good writing and the needs of people to understand technology have not changed, so the rest of the book remains useful.