The Zone

I've been in a bit of a writing slump lately. I know the best way to lose readers on your blog is to write crap. I don't write every day to win a Pulitzer prize, I write every day because of the discipline.
I've read a great deal about writers and there are a few common themes. Read the work of really good writers, study the craft, love the language, and write every day.
Some days the ideas and word flow effortlessly. Some days I have to pry them out with a spoon.
There is no pattern, except I've noticed that writing when I'm really tired is a total waste of time, but it's impossible to predict when the drought will occur. One thing I should do is write several columns and blog entries when I'm in the zone.
I tell you this is a book that would be a hit with struggling writers....What do you do when the words won't come?
Anyhow, I plan to rest up tonight and find the words tomorrow.