If you've ever been bamboozled by a legal contract or attempted to wade through obtusely written government leaflets, you will know the value of Plain English. Writing plainly is easier said than done, however. Fortunately, Martin Cutts provides an excellent guide with this book. Over 25 chapters he touches on such topics as the importance of layout, planning your documents in advance, using good grammar, maintaining consistency in usage/style/punctuation, and adapting texts to different audiences (e.g. the Web, people with low literacy). It also includes a list of pompous-sounding words and their plain-language alternatives, examples of good design and layout, and "before" and "after" paragraphs, many of which were evaluated by focus groups.
Because this is an Oxford University Press publication, some of the usage and style conventions are more appropriate for a UK audience, but overall this is a great resource for anyone writing or editing in English.