Is actually quite a silly question. It’s like blogging, but on a micro level (that’s why it’s called micro-blogging I guess). You basically do what you think should be done. I did brush up on my twitter etiquette lately, as I started expanding my follower count a big, and I didn’t want to piss people off. I have a tendency of only following people that post interesting enough stuff to read imho, and people that don’t over-tweet. I don’t see twitter as an IM tool, but some do, and that’s just fine, but I simply don’t like my feed being swamped with endless trivial conversation with people I don’t even follow.
During my research (read: googling, but research sounds so much fancier doesn’t it?) I did come across some interesting bits here and there. This twitter etiquette guide links to a number of good blog posts on the subject, and this Morning News article definitely has some very good points. Also interesting is Bishop Alan’s post about why twitter is all about the social aspect, and not about technology. It goes back to 1711. Talk about research! I bet he googled it.