Though this book is short, it is very helpful. Jordan begins by identifying the four crucial ingredients to any logline (and any story): protagonist, antagonist, goal, and situation. Using these four bits, he creates two model loglines. After this chapter, Jordan invites readers to create loglines for their own stories: these loglines will be edited and improved as you read through the book, as each chapter ends with short exercises.
Once he's covered the basics, Jordan moves on to the big guns: specific ways to improve your starting logline. Most of these are good ways to punch up the logline: portraying conflict and irony; having a good hook to grab readers; and using the words 'force' or 'must' to up the stakes for your main character. We also whizz through several no-nos, such as a moral or many tangle story threads in one logline.
Overall, Jordan's book is full of good information; not just for writing loglines, but for finding the true core of your story. As the author himself writes, "If you don't know what your story is about in a sentence, you run the risk of meandering your story into places where it doesn't belong." And for $2.99 at Smashwords (link), how can you resist a 50-page guided tour into figuring out the core of your story?
Jordan's book is an excellent read for any writer: his humorous and witty style only adds to the enjoyment. If you're a writer, you should certainly pick up this book and find the core of your story.