Having done a few posts on different kinds of publishing and which kinds to avoid, let me now start by giving some advice on how to start writing in a way aimed at getting published.
1. Most importantly, START WRITING! Don’t wait until you’ve read a bunch of theory before you start. Just start. If you don’t get in the habit of writing–and writing regularly–you won’t get good at it.
2. Be prepared to write a lot of stuff that never gets published. This is your practice work. Everyone learning any skill has to practice, and writing is no exception. As a result, relax. Don’t worry about whether this stuff is good enough to print. Don’t have that as a goal for your initial writings.
3. Become aware of what you read. As you read stuff–particularly stuff you like–ask yourself questions, like: "Why did he say it that way?" "How could he have said it differently?" "Why didn’t he?" "What is it about this writing that I like?" "What don’t I like?"
4. Get some books about how to write. There are lots of them out there, and they’re specialized by the kind of writing your want to do (e.g., non-fiction, fiction, science fiction, detective, romance, western, etc.). Read them.
5. Get the book Elements of Style by Strunk and White. This is a very short book offering concise writing advice. It is the standard work for beginning writers. Has been for decades. It’s also cheap.
6. Start getting feedback on your writing. This is very important, because if you don’t do it, you won’t know how others see your writing, and you won’t make progress past a certain point. Unfortunately, this is also a tricky step.
The easiest thing for most folks to do to get feedback is to hit up their friends and relatives. But there’s a problem: Your friends and relatives (at least the ones you’r likely to hit up) will want to be nice to you. That may interfere with their being honest with you. Honesty is what you need, though, to know whether your writing is succeeding or failing. Another problem is that your friends and family likely are not professional writers themselves and thus may not be able to help you make that much progress.
An alternative that many beginning writers try is joining a writers’ group. Just about every town has these (if you know where to look), and if yours doesn’t, you can start your own. Writers in the group meet, share what they’ve written, and critique it. But there’s a problem here, too: Writers’ groups tend to turn into groups of friends, which raises the niceness vs. honesty problem mentioned above. Worse, writers’ groups frequently end up spending most of their time socializing and comparatively little time critiqing writing. Also, while the writers in your group probably know more about writing than your friends and family, they usually aren’t professionals. Most of the writers who attend these groups are amateurs, and so there’s a limit to how much they can help you progress.
I speak from some experience on that one. I myself used to be a member of a sci-fi writers group. None of us (at the time) were published, and we turned into a group of friends and then started socializing and stopped working as a writers group. I still miss those guys. (Sniff.)
Another alternative is to take a writing class or–better–a series of writing classes. These are commonly available at your local community college. There are also some online. DO NOT NEGLECT TAKING COURSES THAT TEACH GRAMMAR AND PUNCTUATION. THESE ARE VITALLY IMPORTANT FOR GETTING PUBLISHED. Taking courses usually solves the niceness vs. honesty problem, because your teacher typically will be much more honest with your than your family and friends. (In fact, you may be horrified at all the red marks that come back on your homework.) Better, the teacher also probably knows more about writing than your family and friends–and there’s a good chance he’ll know more than the members of your writers’ group, too, at least about writing in general (if not your particular genre of interest).
The ultimate feedback is sending your material off to publishers (for professional publications, not vanity presses). This is the final threshold. If you can successfully get past this one (and it will take some doing), you’ve arrived in the world of professional publishing.
But that’s a whole ‘nother story.
In the meantime . . . START WRITING!