Every writer is different.
That's a good thing, because if we were all the same, life would be fairly boring.
How each writer writes their first draft is also different, despite a few common themes or techniques.
Here's what I do. Ready?
As I've noted before, I don't outline. Even the thriller I'm currently editing, I never outlined it. I'm what is probably called a discovery writer. I write by discovering and do very little planning. Stephen King is like this, even though my skills pale in comparison with his by lightyears.
I set a goal of X amount of pages to write in a single day, then I set out to write those pages. Most of the time, I either meet that goal or exceed them, with a constant urge to exceed. It may take me several months to write, but for the most part I do not look back, except to check a few facts or to make sure all of the details match up. I rarely go back and edit. I resist all temptation to go back and fix something. I wait for that until the first draft is complete.
Not all writers do this. Some edit as they go, but I personally find this too tedious. I'd just as soon get all of the pages out there--I call this vomiting as much onto the page as possible.
Find out what works best for you. My way isn't for everyone. But the bottom line is to dedicate yourself to writing . . . and write every single day.
In the words of the great philosopher, El Nike: "Just do it!"