Don't post 20 times in one day just because you missed a few days the previous week. Many blogging services let you plan posts to go live at set times in the future, so use this feature to spread them over a few days.
Don't post personal information like your address, mobile number or birth date. Identity thieves get everywhere.
Don't delete comments just because someone disagrees with you. Blogging is a two-way conversation, not a one-sided rant.
Don't copy and past other blog's post and pass them off as your own. Obviously.
Don't think you can earn lots of cash by clicking your own ads. Google is wise to this sort of thing. Really
Don't write punning or obscure titles for your posts if there's a more down-to-earth alternative that get major keywords in. It'll make help you get more traffic from search engines.
Don't get involved in pointless flame wars with other bloggers. You might think its sophisticated verbal jousting, but your readers will probably just think its boring.