P is for...Polishing and Publishing. If you want to do one, you have to do the other.
Polishing is the act of cleaning up your writing. This includes editing, proofreading, rewriting, adding and deleting, and working in suggestions. Before you even consider sending your manuscript off to be published or reviewed, you have to willing to do some heavy lifting yourself. While your first several drafts are stuffed full of wonderful things, you still need to go back over it (yes, every last page!) and make sure there are no obvious errors. Use the resources available to you (spelling and grammar checkers, dictionaries, blogs, friends) and clean it up. With all the cutting you have done to get it where you want it to be, you might have left some loose ends.
Publishing is submitting it to a publisher and getting it through all the processes to become a publicly-available work. Basically, this is the big goal (besides getting tons of sales, of course!). This includes following the submission guidelines, going through another round of edits, pulling together a synopsis and other information, and doing all the leg work to get your book past the printing press and into the hands of readers. If you think you are finished with your manuscript once you send it out and don't want to make another change or lift another finger, then don't bother. But if you are dedicated to your work and are willing to do all the heavy lifting to get it to where it needs to be, then you truly have what it takes to be a successful author.
The biggest advice for succeeding in these two areas? Stay motivated and remember why you write!