Whether you're just starting out or are already a prolific novelist,
everyone still has something to learn about the writing process. These
books offer numerous insights useful to budding and seasoned writers
Feel the need to make your characters more complete? These books each
offer a host of different descriptors -- good, bad, and ugly -- along
with descriptions of how they might be shown, why a character may have
them, and what they might mean to your character's development.
For you worldbuilders out there, or those who want to become
worldbuilders, I've found no books more insightful than these from Mark
Rosenfelder. If all you need is a world, The Planet Construction Kit is
all you need, but if you want to go all out and at least come to
understand what languages exist in your world (or even start to create
them!), the others are invaluable!