However, I would add something else that I discussed some time ago in response to pointers about blogging, namely that you should not focus much on rules. This is supposed to be fun, and trying to keep a lot of rules in mind makes it less fun. I like the professional benefits that come from blogging and tweeting, but the real reason I spend time on them is because I really enjoy it (though Jay correctly points out that this is addicting, so maybe I enjoy them the ways addicts enjoy drugs).
As of this moment, I have 8,437 tweets. Many of these are not well thought out, may include dumb pictures, or reflect pure whimsy, while others were about ongoing events in Latin America and got lots of responses and retweets. All of them, though, were fun. So keep your eye on that prize.