While it's important to write a lot when you want to become a good writer, it's also important to take breaks from time to time.
It's probably horrible for momentum, but I find it best for my creative flow to take a minute or two off every quarter-hour or so to let my thoughts drift, use the restroom, etc. as I write. When I come back I can usually hammer out a paragraph and then craft my way further.
Taking longer breaks is less advised. When I don't write for more than a week at a time my quality and inner-editor perception wane. Lately I've been trying my best to not do that.
This being said, I'm ending this post right here and resting from the A-to-Z Challenge until Sunday, when I'll be linking to a dark steampunk/horror story I wrote Tuesday afternoon. Have a good day!