This book, written by a sci-fi author with a PhD in geology, is explicitly targeted at science fiction writers and covers world-building: literally. It is comprehensive in its description of the physics of star and planet formation and will tell you everything you need to know (and possibly more than you want to know) about astronomy, planetology, astrophysics, and chemistry. Short of taking a few college-level courses, you probably can't get a better education that's sufficient to write "hard SF" alien worlds.
Of course, if you don't really care how plausible sulfuric acid oceans or gas giants orbiting a brown dwarf or ice worlds are, this book will be of much less interest; you might take a few details from it and figure that the average Star Wars fan no more cares about the plausibility of your planet's elemental composition than he cares about the fact that explosions don't make a sound in a vacuum. It's still worth reading so that you know more about how Earth's own climate and topography have been shaped over the eons, and why there is no life on Mars or Venus, and all the things that early sci-fi writers got wrong. There are numerous references to classic science fiction novels and short stories: Gillett points out some of the more creative inventions in the literature, as well as some of the more unscientific ones.
This is a very crunchy book: if you want to seriously use the information here to design your own worlds right down to their sidereal rotation periods, you'll need a few spreadsheets. Gillett provides formulas, tables, and an extensive bibliography. It will also help to remember your high school physics and chemistry.
This is all science
for writers, and contains no information at all about writing science fiction itself. There is some discussion of how life forms, and how you might plausibly introduce very alien biochemistries (as well as why many types of worlds are unlikely to evolve anything more complex than bacteria, and why others might evolve intelligent life that probably wouldn't be able to develop much in the way of technology), but beyond that, you'll have to look to other books in this series for designing alien life and civilizations.