Of course, there isn't one resource that tells you all the answers. We have to sift and choose who and what advice to follow. However, you do need to spend a percentage of your writing life reading and studying the ways of the industry not to mention who's still alive and kicking in the industry. My personal advice to you . . .
1. Pick one writer's magazine and subscribe. The most obvious in the USA are Writer's Digest, The Writer, and Poets & Writers.
2. Pick a reference guide for agents and/or publishers.Writers' Market is one - both online and in book form. But so is Publishers Marketplace since it lists current information, updated daily. Guide to Literary Agents is great.
3. Select one reference guide for magazines and periodicals. The Best of the Magazine Markets for Writers is one of my favorites. Writer's Market already listed above is also good. I also like the online database of Worldwide Freelance. It is international in flavor, but also covers US markets. I find it maintained well.
4. Pick three newsletters or blogs to follow. Follow them for a month. Then choose three more, culling those you already had that aren't doing you any good. Do not get caught up in trying to read them all. Pick a day a month in which you analyze whether to keep or add new resources like this. Find ten tops, unless you are writing full-time. These can be genre related, as in fantasy or children's writing. Or they can be marketing related, or self-publishing related. Just don't think you have to follow everyone. Be selective.
5. Join a writer's organization. Don't try to join a dozen. You won't have the time to become active in more than one yet still find time to write. Society of Children's Book Writers & Illustrators if you write children's books. Science Fiction and Fantasy Writers of America - Mystery Writers of America - International Thriller Writers Association - Romance Writers of America. There are groups for copywriters, journalists and editors. Go to my website and look at Professional Organization on a hidden links page I still maintain. You'll find dozens.
Yes, there are gobs of resources. No, you don't have to subscribe to all of them. Pick and choose. One magazine, one database, one resource book, one writers organization. You need to stay somewhat up to date, but you don't have to become an expert. Writing is time consuming, but if you don't know what to do with it once it's written, then where are you? Just know enough to know where to look when a need arises.
GIVEAWAY NOTICE: I'd like to give a gift subscription to Writer's Digest Magazine to one lucky commenter.
UPDATE - WINNER: Steve Spohn is the winner of the Writer's Digest magazine subscription. Congrats, Steve!