My best advice

1. Check out the blogs I read, see what other writers have to say about writing. These folks offer a ton of advice and inspiration.
2. Let a friend read the first dozen pages of your work to get a reaction. If they want to read more (and you’ll have to judge their sincerity), you’ll know you’re on the right track.
3. Join a writer's group. I'm not a big fan of this recommendation so BEWARE. Find a group that will offer critiques of your work and offer your critiques. Stay away from a group that's just looking for pleasantries.
4. Practice summarizing your work the way you’d like to see it featured in the publisher’s notes. If you can’t do it in 200 words or less, try again.
5. Write a practice query letter. Convince an agent/publisher to take you on as a client.
6. Keep writing.