First and foremost.
I've been reading through countless emails that have suggested coming up with a book idea without writing the book . . . then submitting this to agents and publishers. I personally couldn't conceive of doing this. Getting plot, structure, characterization, and dialogue correctly is something you can't just create in a matter of days. Writing isn't easy regardless of what you say or other's say. It takes so much time and effort to create a book. Those of you who have completed your book - my hats off to you.
Finish the book. Finish the book. During my book signings, I can't count the number of people who have come up to me to tell me they've been writing a book for years but haven't finished.
If you're like my friends, you generally put the book down then come back to it for a few days eager to start. After a few days you toss it into your very own little slush pile for a few months. When you decide to come back you go to the beginning and make changes without ever finishing the book. It becomes a merry-go-round circus in which you tell yourself next week is that day when I start (in earnest) on the book.
It doesn't work. Finish the book!
No more excuses, no more changes! Finish the book!