Since we were already on the topic of J. Steven York, he has a great (long, but worth it--I promise!) post on tweeting.
"The two most important social networks are Facebook and Twitter. While everyone including your granny seems to find Facebook easy to grasp, for some reason Twitter is much more intimidating. It’s relative simplicity - text-messages, readable by everyone, but limited to only 140 characters - provides little structure or guidance as to how Twitter is best used. It can leave even the most prolific and confident of writers staring at the screen asking, “What should I post?" . . .