Vagueness and Internet Privacy

I'm never sure how vague I want to be online. How many details do I give out, not just about me but about other people? Do I use nicknames, initials, first names only? I'm still working on that. I hear all sorts of horror stories about internet stalkers and whatnot, but honestly I think the only people who are going to read this are people who already know me, and there shouldn't be anything too personally inflammatory in it. If there is, I'm doing it wrong. I think I'll do first names only - people who know me then will know who I'm talking about, but people who don't....won't.