Step one: WRITE IT!
Step two: edit and revise the hell out of it.
Step three: Submit or query it. BE SURE TO FOLLOW THE SUBMISSION GUIDELINES! !!!! I cannot emphasize this enough.
Step four: write something else while you wait for a rejection or acceptance from the publisher or agent you sent it to.
Step five: Repeat step two. If it was accepted, you’ll do this with editorial feedback. If it was rejected, you’ll do this to prep it for a different editor, agent, or publisher.
Let the waiting game begin.