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.
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.
Encourage visitors to post comments. And join the conversation. Visitors to business blogs generally want one thing--to be heard by the business.
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.