Although the most important thing about writing is the act of writing (and lots of it), there are books that can help with writing better. That way, you can "work smarter, not harder," which is also known as "not flailing at the keyboard like a monkey."
No offense to monkeys intended. Some monkeys may be super-genius monkeys. Your monkey may vary. I digress.
These books are for "new-ish" writers because it can take years to get published for the first time, or years between first and second publications, so a person can be a rather experienced writer while still struggling with questions of how to write stories that editors will buy. I haven't read all of the writing books in existence, but I've read many of them. Here are five of the books I consider to be the most useful for the earlier stages of learning to write fiction (and re-readable, because you can get more out of them over time).
How to get writing into your life and keep it there
Page after Page, by Heather Sellers: This is the only writing book I've read that gets into the subject of why you want to write in the first place. Lots of people think they want to write. Do they really? Do you? Once you have that all figured out, the book covers the importance of regular writing practice, and includes ways to keep yourself writing even when you don't feel like it. It also does a great job of explaining why it's important to interact with other writers, and how you can do a good job of that. This is the book that convinced me to start going to conventions, and going to conventions is brilliant! (I will definitely write a whole separate post about that sometime).
How to actually create a story
Creating Short Fiction, by Damon Knight: This, in my opinion, is the best basic, how-to-write-stories book. By "basic," I do not mean "for beginners only." You can read it, and then go forth and write stories for a while, and then read it again and get more out of it because you'll be at a different point in your writing ability. Many writing books get into the same topics as this one, but don't explain them as well.
Writing Fiction: A Guide to Narrative Craft, by Janet Burroway: Each chapter of this long-lived book includes discussion of a topic in creating fiction, as well as at least two short stories that demonstrate that topic - such as characterization, atmosphere, or structure - done well. The chapter on revision contains stories by Heather Sellers, who wrote Page after Page, listed above. DO YOU SEE HOW THIS ALL CONNECTS TOGETHER IN THE SCHEME OF THE COSMOS? Ahem. Got carried away there.
From Idea to Story in 90 Seconds, by Ken Rand: This is a short but absolutely excellent book about getting ideas, making them distinct from everyone else's, and developing them into the kind of stories you want to write. It's entertaining, it won't take long to read, and it's all good, useful stuff. If you tend to have trouble with knowing what to write, start here.
How to tighten up your prose after you've written a story
The 10% Solution, by Ken Rand: Another short and completely great book. This explains the reasons for editing unnecessary words out of your stories (and any writing that you do, really) and then leads you through an easy system that will literally cut at least 10% of your words out, unless you're already writing like Hemingway. Raise your hand if anyone has ever said you wrote like Hemingway. If you raised your hand and your work is getting published in venues that pay you money, please stop reading this, start writing a blog about how you do what you do, and send me a link to it when you're done. Thanks in advance! If you didn't raise your hand, be like me and use this book's system to cut out extra words, which will make your story easier to read and harder to stop reading. That's the goal.
Bonus! Not a book! How to put a story into Standard Manuscript Format before you submit it (but only do it this way if the guidelines don't tell you to do it another way)
William Shunn : Manuscript Format : Short Story
No two people will get the same things out of a given book, but my opinion is that there's always something to learn in good books about writing, even if you're going back and reinforcing ideas that you've heard before but never completely internalized. The main thing to remember, though, is to read about writing a little, and write a LOT.