Copyblogger has a nice, concise list of tips on how to recognize when your blog post is quickly going down in flames. While these tips follow the basic, timeless tenets of good writing, well, even good writers often forget said tenets in their blogs.
Tips with excerpts:
1. What’s the Point?
The worst thing a reader can be thinking after reaching the conclusion of your post is “What the heck was that all about? 
2. Who Cares?
The worst thing a reader can be thinking early into your post is “Why should I bother with this? 
3. Bad Chi
Bad flow makes for bad narrative and confused readers. Be sure that your sequence of ideas is both logical and compelling…
4. Detail Dump
Don’t go off on tangents that unnecessarily drill down too deep. That’s what links are for…
5. The Rambling Road
Don’t listen to the people who say you should never write a blog post over 250 to 400 words. Any piece of good writing is as long as it needs to be, but not one word longer…
