There’s an excellent article I came across a couple of days ago on Matt Cutts site all about the things you shouldn’t do or write about on your blog. I’d sincerely recomend reading the article in full, but here’s a brief summary:
The easiest time to make a blogging gaffe is when you’re starting out.
Don’t criticize other companies or people.
Don’t post when you’re angry.
Learn which stories matter and which ones don’t.
If you make a mistake, don’t clam up.
As I said earlier, I’d seriously recommend all bloggers read the article in full.