Just finish the book!! Don't let insecurities about whether it's good enough or whether you're "doing it right" stop you. The magic happens in revisions. And find a good critique partner or critique group. No one can be entirely objective about their own writing-- another set of eyes is so valuable. It also prepares you for the submission process. Organizations like RWA (and its local chapters) are the perfect place to find these great writing buddies. Writing itself can be an isolating process, but you don't have to take the journey alone!