William Evans in his well written book on "How to Prepare Sermons and Gospel Address" discusses the theory and practice of preparing sermons. Evans focuses on methods, outlines, guides for study, the use of illustrations, and the selection of texts.
Evans' book is marred by two things. First, it is rather dated. My copy was published in 1913. By itself a hundred year old religious book is not automatically outdated but the way this one was written, it does limit its modern day effectiveness. Second, and marred is probably the wrong word here, it is rather limited by its extent. It is a relatively simplistic summary of decent advice regarding preaching. He delves into no Scripture, and gives precious little of the why behind the what, though what he does give is good.
By the same token, the book is by no means a loss. In spite of its limitations it contains numerous helpful nuggets, especially for younger or lay preachers. It helps that Evans knows how to write a pretty turn of phrase now and again.
Worth reading? Depends who you are and where you are at. Contains good stuff? Sure.