Courtesy of Inc.com:
1. Bare it all
You don't have to give away trade secrets, but effective blogs require a certain amount of candor. There's nothing more boring than a blog that pulls its punches.
2. Update frequently
Content gets stale fast online, so refresh the blog at least three times a week, if not more often. And mind the spam in the comments section--business blogs get tons of it.
3. Be interactive
Encourage visitors to post comments. And join the conversation. Visitors to business blogs generally want one thing--to be heard by the business.
4. Stay cool
If commentators get nasty (and if your blog is any good, they will), don't go on the offensive. Engage them in conversation. And wait it out: There's always a new controversy around the corner.
I figured out #2 & 3 pretty quickly, although I'm not sure if it's making a huge difference. Of course, I have a little different spin on #4, but that's just me.