These writing resources have been totally invaluable to me as I learned to be an author.
It's hard to write alone in a vaccum. I don't know what I don't know. Something may be perfectly clear to me because I knew what I meant but unclear to anyone not locked in my brain. Critique Circle has helped me tremendously by giving me a place where other writers can evaluate my work. I've also discovered that I learn a lot and enjoy critiquing others.
The Emotion Thesaurus by Angela Akerman & Becca Puglisi
Show don't tell. Everyone tells you to do it. This book gives you lots of ways to do this for a person's emotions. It is the one book I keep beside me while writing. Here's a link to the book on Amazon.com.
Using synonyms can really make your prose pop. There are lots of online resources to find synonyms but over and over again, I find myself returning to thesaurus.com.