1. Finish a book.
Really. Stop starting every shiny new idea that flashes into your brain and find the discipline and perseverance to type one idea all the way through to The End. It won't be perfect. It probably won't ever be published. But what you'll learn about yourself and the process will be invaluable and every subsequent lesson on craft will make a lot more sense.
2. Don't be so eager to share your work with others.
Not yet, at least. It's important to protect the creative process and the shape of the story itself and staying away from too much outside input until you're sure of the story and the characters is a good idea. I write and write and write ... until I know exactly where I'm going and how I'm going to get there and THEN I invite critiques from my CPs. And if you're posting chapters of your work willy-nilly on your blog/site/facebook page, stop. Editors are leery about selling a book when much of it has already been offered for free.
3. Less talk, more typing.
There are many ways to network with other writers and I agree that for most of us, that's an important resource. However, many newer writers spend more time talking about writing than actually writing. Most of my author friends have time limits for how much we can spend answering email, blogging, typing on Twitter etc. And all of us have word count/page goals etc. that come FIRST. Write more. Talk about it less.
You'd think this would be a given, but I often talk to newer writers who rarely read. This is foolishness. For one, reading within your genre gives you a firm grasp of the genre and what's already been done to death. Reading outside your genre gives you inspiration for new ideas you could bring to your genre. For another, it's wise to read the books you're secretly afraid you'll never be good enough to write because that's where you absorb craft and, if you let yourself, become inspired. And finally, publishing is a small world. You'll feel like an idiot if you meet a prominent author in your genre at a conference and have no idea what they've written.
Set the scene. Explore the emotions. Record the sensory detail. Don't be in such a hurry to get from point A to point B that you neglect to deliver the entire scope of the scene to your reader. If you don't know how to linger without filling your pages with exposition--fill your pages with exposition. Get it out there. You can trim it down later when you've figured out exactly what needs to be said.
6. Understand that writing is largely about revising.
And revising is often harder than writing the first draft. Your novel won't be perfect the first time around. It will have clumsy phrasing, awkward pacing, missing words, lack of setting, characters whose motivation is as clear as mud, exposition where there should be action, and plot arcs that manage to get run over by a bus halfway through the book. It doesn't matter. What you didn't learn about craft by finishing your first draft, you'll learn by revising.
7. No book is ever perfect.
There's always something you can change. Another layer to add. A scene to flesh out. A question to answer or one to raise. There are no perfect books but there are excellent books and the trick is knowing when you've hit that level and can let it rest.
8. Some books won't ever be published but you should write them anyway.
I know you think the book you're writing NOW is the one. You may be right. Then again, you may be wrong. It doesn't matter. What matters is pushing yourself to write the very best book you can and then surprising yourself with how much better you can make it through revising. No finished draft is ever a wasted endeavor. You might type The End and think you've reached the pinnacle of what you're capable of accomplishing but you'll look back in two years (IF you continue writing) and wonder at how far you've come.
9. Self-doubt comes with the territory.
I've come far enough along in my career to be privileged to call many published authors friend. All of us share one thing in common--we worry that we won't measure up. We worry that we will. We worry that no agent/editor/reader will snatch up our book and when they do, we worry they won't like it. When they do, we worry our next one will bomb instead. You can't get rid of every shred of doubt and you don't need to. The trick is to answer the doubt with action. Keep your head down and write. Take praise and criticism with as much humility and wisdom as you can and then write some more.
10. Interest and inspiration start books. Determination, perseverance, and stubbornness finish them.
If you're waiting for your "Muse" to return before you discipline yourself to write, you won't finish your book. If you want life to slow down, your schedule to clear, or the people around you to suddenly come to their senses and support your passion before you make the commitment to finish your book, you won't finish. It takes guts to push past the sparkling beginning and dive into the meat of the story. Finishing a book takes giving up sleep, turning down invitations, and refusing to watch tv so you can write instead. Finishing a book means writing a scene that refuses to go smoothly even though you'd rather do just about anything else. If you want to turn your writing from hobby to career, find the determination, perseverance and stubbornness to finish a book.