I have looked through writing guides, how-to-write books, writing blogs, etc.... and so far, the best advice that I have discovered is from a youtube video of one of Stephen King's interview. One of the people in the audience asked him what his best advice was for aspiring writers, and his advice was:
To Read Alot and Write Alot!
And this is the best advice for any writer. ...I'm serious. This is the best advice out there for aspiring writers. I know it sounds simple. And guess what? It is simple. This advice is the magic pill of writing. Just because it's not complicated or super specific doesn't mean that it's not really good advice.
I'm willing to bet that most famous writers out there are people who have read a lot of books since they were little kids. Plus, they must have written some stories as well, before they even tried to get published.
Okay, let's break this down:
Read Alot!
-To someday be a great writer, you have to know that you're writing something for other people to read. So, read some other books. Alot of other books. Learn the rules, get in touch with characters, follow the plot, etc... You see, reading is a lot like... umm... I think baseball's a good example. Let's say someday you want to be a famous baseball player. Well, you can't be a baseball player if you've never seen a baseball game in your life and learn the rules of baseball. So, you can't write a great novel if you've never read a novel in your life (and be sure to read a lot of novels!).
Write Alot!
-To someday be a great writer, you also have to write a lot. Practice makes perfect. I'm not going to lie, your first few attempts at writing will probably be failures. Do you think the first stories that Stephen King wrote or JK Rowling wrote was published. They have written stories that the public will probably never see. It's like that baseball example. In baseball, it seems simple because all you have to do is catch the ball, throw the ball, hit the ball, etc... It seems simple, just like writing seems simple. If you've read a lot of books, it would seem like you can write a book as well. Guess what? It's harder than it looks. Again... Practice makes perfect.
Since I believe that this advice is the best out there, I'll type it again:
To Read Alot and Write Alot!