Read Nathan Bransford's blog today, When It Feels Like There's Nothing Left to be Written.
There is no problem facing a writer that can't be solved with more writing. It's a weird dichotomy. On the one hand you have to be brutally honest with yourself and recognize that you're not perfect and no matter how good you are, you're writing could be better. (But that's for the rewrites.) On the other hand, you've gotta keep plugging away, trusting with almost childlike innocence that eventually all that typing will turn into writing and, with some work, you'll have a good book.
Back to plugging away.