BELIEVE IN YOURSELF - BUT WORK HARD
In a world where bad news dominates the airwaves and internet, the one thing a writer needs is belief in themselves. The publishing world is full of rejection. Agents send them out even when a writer just sends a simple one page query, and editors send them out when a chunk of the manuscript is sent. Writers learn early on that they must have thick skin. This is not a business for the squeamish.
If you truly want to be a writer--a published writer--then you need to have a tremendous amount of belief in yourself and in your writing.
Now, this isn't to say that if you query fifty agents and they all tell you that you need to work on your craft, that belief alone will make you a better writer. Now you're just living in fairy world. Once in a while you will actually get a rejection that gives you advice. Take it. If the agent says, "Great concept, but poorly executed." Well, you need to take that as you need to do some work on your craft. Take a college course in Fiction Writing. If that doesn't fit in well with your life, consider taking an online writing course.
When I first started out, I realized that the last "English" course I had taken that had anything to do with writing mechanics had been in high school. AND, that course didn't tell me any of fiction writing mechanics. Realizing this lack, I took a few courses through Writers Online Workshops (WOW). I learned about point of view, scene and sequel, characterization - all the things that I did not learn in high school and college. Invest the time in yourself to work on your writing. If you have grasped all of the technical parts of writing, then join a critique group. Be warned though; people can be cruel, especially if they are jealous. Pick a critique group that gives positive criticism only. Negative criticism will only create self-doubt.
There are many non-fiction books out there about writing. On Writing by Stephen King is wonderful, and I highly recommend it. Writing Down the Bones: Freeing the Writer Within by Natalie Goldberg is another great book. If you don't have the time or money to take a class, a good writing book can be a great substitute.
Read, read, read. Reading the genre you write will make you a better writer. BUT, you have to start reading with a different eye. If you pay attention to the mechanics of published works, you will learn a lot. Unfortunately, though, the more you read, the more you critique and sometimes it's hard to get lost in a story. Being an editor by day, it makes it very hard for me to stick with a book. If I'm not captured fully within the first chapter, the book goes back to the library.
What have you done to help hone your craft? Reading books, taking classes, a critique group? I'd love to hear what you've done.