Kobold Guide to Game Design, Vol. 2
The first KOBOLD Guide to Game Design was a sleeper hit, compiling advice from Wolfgang Baur, Ed Greenwood, and Nicolas Logue on how to think about different genres, how to improve your game as a DM, how to make a setting come alive, and how to use design compression to strengthen your work.
And the second volume has now been announced for preorders, and it is even better.
This volume contains more than a dozen crucial essays to help you succeed in freelancing, playtest, and publication, including: