Many people have asked me for writing advice, and as someone who is much better on paper than I am in person, I never know what to say. Thus, I have come up with a list of some writing resources that really helped me (and continue to do so because each book is different and requires different choices).
Writing Excuses Podcast -- seriously, listen to the archives. You'll learn so much.
K.M. Weiland's book, Creating Character Arcs -- I didn't really understand character arcs or how important they are to the story until I read this. Actually, any writing book by K.M. Weiland is worth a read, so go check it out. She also has good advice/resources on her website.
If you're about to query agents or editors, check out QueryShark, and yes, read the whole. entire. website. You'll know how to write query letters, but you might even find something glaringly wrong with your story, like I did.
Pixar in a Box's The Art of Storytelling, a free series of video lectures that take you behind the scenes of how Pixar creates their beautiful masterpieces. I recommend the first three sections on story, character, and structure. The others are more for filmmakers and animators, but they're worth watching if you're interested.
Aside from that, here are some rules of thumb I've picked up along my journey to publication:
If you're feeling insecure or unsure about something, you're almost always right.
Getting others to read my book and give me brutal feedback was the most effective way I grew as a writer. It is also the best/fastest, but most painful way to fix any broken story. This comes with the caveat that not all feedback you receive will be right, but they will at least show you there's a disconnect between your writing and the reader. Find what it is and fix it in a way that is true to you and to the story.
Write the truth. Don't write what you know. Because what do I know about fox demons and heavenly fairies?
Writing hurts. Editing hurts. Receiving feedback hurts. You will go through the stages of grief. Feel it, live it, get over it, come up with a plan, and get back to work.