In a nutshell? Finish your first book... No matter what it takes, no matter how bad you think it is. Why? Writing requires untold amounts of discipline and the first discipline is the most important. Finish the project.
The finished project can be cleaned up, edited, scrutinized, chucked in the trash or nominated for a Pulitzer. An unfinished manuscript is a burden, a reason to stop, a reason to doubt yourself, a reason for your detractors to say "I told you so."
Do you remember Tom Hanks in Castaway? "Look what I have created! I have made fire! I. Have. Made. Fire."