This book is a classic guide to writing English clearly, by Ernest Gowers, a leading civil servant of his day (the original edition was published in 1948). It has been well revised and updated by his granddaughter, Rebecca Gowers.
It was aimed at civil servants, but for the most part its analysis and advice is useful to anyone interested in clear writing, be they reader, writer or neither. Gowers was not an academic linguist, but a deeply engaged practitioner of official writing and on this evidence a very well read and most thoughtful, lucid and practical man.
He practises what he preaches: he shows with great clarity what the questions are, what problems they can give rise to and why he recommends his preferred solution (where he has one, which is not in every case).
He has a lot of ground to cover, and he covers it concisely: the only boring sentences in his book are some of his examples of bad writing, and once he has made his presentation and argument, he moves on to the next point.
He is reasonable rather than dogmatic. He doesn't shy away from judgement as to what is good and what isn't, but where he sees that some point is unimportant, or irremediably arbitrary, or impossible to decide, he is happy to say so. He strikes a judicious and informed balance between the demands of logic and the facts of how things just happen to be.
He does not try to play the comedian, as some writers in the field do, as if embarrassed to be writing on a subject they fear readers may consider dry (stand up, please, Benjamin Dreyer); yet he is sometimes drily funny in passing.
Still less does he make his theme into an ideological hobby-horse (hello, David Shariatmadari). Instead, he keeps his focus on the task at hand: helping officials to write clear English for the benefit of readers who are the subjects of rights, obligations, restrictions and authorisations, which is to say everyone.
He makes you notice what your own faults are (one of mine is over-use of parentheses), which is obviously necessary if you're to have any hope of curing them.
Keep this book on your desk and refer to it as needed, which is likely to be often; but take it to the beach with you too.
A quick word on the update: it's pretty good. Language changes: Rebecca Gowers has removed some outdated material and introduced a small amount of supplementary new material, in the form of comments on Ernest's subjects rather than of independent new sections. There is an interesting preface, which tells us a bit about Gowers' interesting and impressive life as well as about the subject and history of the book.