Scott Rehm aka The Angry GM has some of the best GM advice you can find on the many and varied internets. And now he's gathered the best of that advice into a neat, concise book on how to RPG. A lot of this book is based on material from his site, so technically you could get it all for free if you poked around enough. But the book form is a well compiled, revised, and edited narrative designed to flow cleanly and clearly from "I don't even know what an RPG is" to "how to run a great campaign".
Some people get turned off by the acerbic writing style he uses on his site, which is a parody of the fabled extreme-adversarial just-kill-all-the-players GM of meme legend. First, those people are wrong and cutting themselves off from great GM advice. Second, the style is toned down a lot for the book and played much more for laughs. So even if you don't care for his site, there is still a lot for you to like about his book.
And there will be something for you to like. If you're new to tabletop roleplaying, I can't recommend a better resource to get you started. To be fair, I haven't actually read any other books on getting started, but this book really is very well built in how it introduces each concept and builds on itself. It also helps new GMs by cutting through fluff and focusing specifically on techniques that will keep your games flowing well, even when things go off the rails. And even if you are a fairly experienced GM like myself, there are probably some new things here you can learn. Scott has a very cerebral and technical approach to gaming and his advice will make you rethink your own approach to your games.
In the interest of full disclosure, I was a Kickstarter backer for this book, and I absolutely feel that I got more than my money's worth for making this book happen. I gave a copy to my nephew, and now he's excited to be setting up his own game for his school friends. I'm not sure there's a better testimonial than that.