The list of How-To books for writing can be daunting—everyone has an opinion. There are a lot of them out there, a lot that are no good. And even worse, there are a lot of good ones too. It's really a personal choice. Which is why you must know yourself before you seek outside yourself.
However, that said, my go-to how-to resource for any writer is simple:
Sure, it gets complicated after that. Merriam-Webster or Oxford?—don't do Oxford; it's for British English—online or book form?
I confess, I kept a dictionary from college for years and relied on the analog version heavily. But after such heavy usage, it could hardly stay together anymore. So I subscribe now to the unabridged Merriam Webster dictionary online. And I get the M-W Word of the Day sent to my email. It's usually the very first email I get every morning. And that makes me very happy.
So while I think most how-to writing resources out there are not needed, the dictionary (and with it the thesaurus) is indispensable. With this invaluable resource, I get to learn the base of words and its history—and with that knowledge, I can also decide if I want to throw it all away and give an old word a new twist. But I can't do that without the confidence of what a word means to start with, and if a better word already exists. (Not to mention if I'm spelling it right.)