I tell my writing students that they should not wait for "inspiration" to write -- after all, if you wanted to be a professional pianist, you wouldn't practice only when inspired, would you? You'd have your butt on that piano bench every single day. Writing is similar.
Nonetheless, I've noticed that there are moods in which I get more done than in other states of mind. The primary factor determining daily word count is how the work is going, but moods contribute, too. Specifically, I get the most done -- and this applies to other kinds of tasks as well as writing -- in one of three moods.
The first is a high-energy, but not truly jubilant, mood that I attain all too rarely, being naturally a low-energy person. In this state everything seems easy. This happens maybe once a month.
The second is the adrenaline rush of a sudden deadline. I don't like to leave things till the last minute, but if a deadline comes from nowhere ("Can you get these galleys back to us by Thursday?" and I'm attending an out-of-town wedding, taking my dog to the vet, and teaching), it galvanizes me.
The third productive state, however, is unexpected. It's when I'm expecting a bad-but-not-disastrous day. My expectations are low: of pleasure, of accomplishment. I just want to get through everything. Surprisingly often, this ends up resulting in a lot getting done, and done well.
What does not get things done is the most pleasant of personal moods: laid-back enjoyment, at-ease well being. Then I tend to dawdle and postpone ("Let's have another cup of coffee and talk some more.") Somehow, the best life has to offer is not the most productive state for me. Seems unfair! But so it is.