Good questions, and believe it or not there are some pretty simple answers. Much easier than finding your way through a maze.
One way to improve your writing or to just begin writing is to write. Yep, that simple, that direct. Write something every day. Whatever your writing interest, make sure you put words up on a computer screen every day. Some days you'll love what you other days you'll hate it, but hey, that's what revision and rewriting is for - curing that hate. All that writing keeps you primed to write some more. And you'll be amazed at how your brain begins to work, how you begin to compose in your head when you're doing other things. Something else to write - notes on all those great thoughts. But don't let keeping notes throw you off track. Remember your goal is to actually write.
Number two. This one is important (well, so are the others, but this one really is important). Finish what you start. Your Mom undoubtedly told you this on subjects other than writing, but it applies here just as well. Insert a bit of discipline and do it. Yes, there will be the occasional time when it just isn't worth the angst to finish a particular project, but that is extremely (let me repeat that - extremely) rare. The simple fact is you can't give up each time the writing gets tough and you can't quite figure out where to take the story next. And, you can't quit one project every time a new idea crops up. If you do, you'll never finish any story you begin whether it's a novel, a short story, a script, or a non-fiction book. (see discipline above). Make it your goal to finish everything. No one reads unfinished anything.
For my third offering I suggest learn the rules. Writing is amazing really. Once you have the basic skills of language writing can be greatly self taught. Read - a lot. Read fiction if you write it, non-fiction, books on writing, blogs, author's sites, whatever you can. Pick up tips and information. Learn more, always learn. Maybe find a mentor, though I admit great mentor relationships are usually stumbled on by chance. But if you don't look for that exposure you won't stumble on that chance. So, sometimes get away from your computer and maybe take a class at a local college or join a reader or writer group. I do have a shop at Amazon where I continue to accumulate good books for writers along with software suggestions; things I've read, used or had highly recommended to me. Yes, I do get a commission on a sale there, but you can find many of those books at your local library too if your budget is tight. Or with the holiday season approaching you might ask for a book you want as a gift purchased at a local book store (especially if you have independent book stores in your town). So read, learn, write.
And my fourth and final suggestion for today is break the rules. Well, hell, you have to know what they are to break them, that's why I mentioned the learn the rules idea first. Once you have a solid understanding of what it is you want to write, the basics of fiction, the innards of non-fiction, the form of scriptwriting, don't be so locked in that you're afraid to go beyond their present confines. Style, format, method, it all changes over time. It evolves because if it didn't, if it stagnated, writing would die. Just look back at the 'classics' of fiction. Stuff written by H.G. Wells, Edgar Rice Burroughs, Jane Austin, Charles Dickens, John Steinbeck, Leo Tolstoy - you get the idea. The writing was different, the style much different. The basic rules have been proven to work but that doesn't mean they can't be changed, broken, stretched.
So have at it boys and girls - go forth, learn, create, break, finish, create again. These four basic habits will take you far. Tell me which ones you stick to and, though I like to keep things simple, which ones you use I haven't mentioned.