"You must write your first draft with your heart. You rewrite with your head."
- Sean Connery, Finding Forrester
That is what you must realize when you write. That you are writing straight from your heart and you don't ever think for a single moment.
A lot, and I mean a lot of people try to find out how J.K. Rowling made such a success with Harry Potter. It wasn't because everyone loves a fantasy. It wasn't because of magic. It wasn't the fact that it was a classic kind of story. It was because it was from the heart, the deepness of the soul of J.K. Rowling.
If you watch a single documentary on her life, you can find that everything there is to love about the book is drawn from her life and soul.
Realize that this isn't about becoming a witty writer or selling millions of copies of your novel. Those aren't necessary results of writing. They're generally a result of writing a) what's popular or b) what comes from your heart. Which one do you want to do?
A great many authors, and successful ones at that, simply pump out what's popular. These authors make money, they get their fortune, their success, they get themselves in the public eye. At least for a fleeting moment until the popularity of the genre fades and the authors themselves fade into obscurity.
But people who have truly succeeded, people like Rowling and Tolkien and Lewis and Chesterton, all have written directly from their heart, and you can find no better fiction than this kind. I think that as a writer I have missed the mark in the past and I've tried writing what's popular instead of what's in my heart. But those are the manuscripts that gather dust on the shelf, their only use now being bookends for my better novels.
So ignore all other advice and write your first draft with your heart and ignore your head. Your head isn't good for much beyond the physical and observable, the math and sciences. Your heart is the place from which creativity springs, and make sure to not let one ounce of that creativity go to waste. Not everyone has it in the ample supply as you, and there must be enough to go around.