A quick tip for for increasing your writing productivity: Keep a word count.
If you measure your daily writing output you have a base line to start from. You can find out which days are your stronger days and which ones are weaker. You can build strategies into place to help get you through the days when your writing suffers a little more. Or at least stop beating yourself over the head for not writing as much as you think you should.
Write hard, write fast, write often, and measure.