My wife, Kristen, passed the Praxis test for her teacher certification with a score in the top 15% of all people who took it. On her first attempt at it. Was I surprised at this result? No. She is earning her Master's degree in Special Education. One of the requirements of this program is for her to attempt to pass the Praxis before completing her degree, yet in the fall she thought that they expected her to pass it before completing it. So she signed up immediately for the next test date. Even though that date was before she took the classes that typically cover the content for the test (she's taking them right now).
What does this have to do with writing? Everything. How did she do it? Good old fashioned hard work and discipline. During the six-week break she had off from classes between Thanksgiving and New Year's Day she organized a brutal study schedule... attempting to put in at least three hours a day of study time, every day except for Thanksgiving, Christmas Eve and Christmas Day. And despite the numerous distractions of our crazy household, she managed to do it most days. Either by getting up extremely early, taking advantage of kids' being out of the house, or studying after everyone else went to bed.
If I devoted even half of the amount of time to writing that she has to studying, I would have a dozen books under by belt by now. Excellence of any form in any field requires many hours spent hitting the books, running miles, hitting baseballs, diagnosing patients, laying bricks, or (in the case of us writers) time spent with our a$$ in the chair... writing.