I have been roleplaying and GMing for a long time, and I had no idea how much I have needed a book like this. Although my style for preparation has evolved over the years, up until recently I hadn't found any truly good advice on how to actually write and prepare good adventures. As Ben Riggs suggests, writing for a tabletop RPG is its own thing and writing fiction for other media (books, tv, films, etc.) doesn't really translate as well as one would hope.
Ben's book is clear, concise and to the point, and provides many "play plans" (i.e. worksheets) for setting up an adventure, whether it's just you and your friends around a table, or if you're trying to write supplements that will eventually be published for a wider audience. The book is filled with solid advice to help you hone your writing, but also to make sure your game is focused on the players and what is actually relevant to the game. The advice is simple and easy to remember (eg. "Problems not Solutions") and I think represents a sea change in the way many GMs have approached writing adventures, at least in so far as I have experienced in my years in the hobby.
You can find lots of great advice on the internet instructing one how to be a better roleplayer or gamemaster, but I would say if there's a single book for understanding how to write better adventures (which your players will actually enjoy), this is it. It will change the way you think about writing and prep, simplifying everything and making the games you run tons more fun in the process. I myself have used these techniques and they definitely are paying dividends. I'm not spending quite so much time on extraneous elements that will never see the light of day and what I have is flexible enough that any plans I do make still survive contact with the PCs. This book is a must read.
If I were to offer any constructive criticism at this stage, it might be to provide a slightly clearer matrix of sorts for the playplans/worksheets or provide iconography to better help identify which ones are relevant for a particular adventure writer. I actually really like the simplicity of the design and layout, but future versions could perhaps benefit from some minor changes and updates, perhaps.