Otherworlds: How to Imagine, Paint and Create Epic Scenes of Fantasy by Tom Kidd. ★★★★★
I found this book very helpful. One of my pet peeves about art books is that they often show you only step by step guides to a specific piece. However, this book focused more on the different elements that make up a piece (lighting, composition, color, water, clouds, ect) than on how to create just one piece. Basically, it provided a lot of helpful advice on how to create a piece. In addition, there were some step by step guides on specific pieces (for those who like that kind of thing).
As the title says, the book focused on how to create fantastical worlds. One of my favorite parts was when the author went through creature design.
I highly recommend this to all people who are interested in creating fantasy or science fiction artwork.
One of the gorgeous paintings included in this book: