One of the ‘must have’ things authors should have is a subscription to Writer’s Digest. I normally don’t believe in sharing or pushing for this sort of thing, but I subscribed, and find every single magazine offers some valuable insight in the writing field.
Their web site is also huge, with lots of articles, an online community, competitions, education, and so much more. Most of which is free. The workshops I think are a bit pricey, but most everything else is great.