Too many of the bloggers of the world either think no one is reading their blog or everyone is. If you're journaling for yourself, okay, but if you want to share you thoughts, you need to be clear.
Besides the grammar, spelling and sentence structure mistakes that confuse readers, too many bloggers assume the reader knows what they are talking about. Not so.
When many of us pull up a blog we're lost. There isn't any background or context to give meaning to what's newly written.
Bloggers need to find a few words to explain why the reader should be reading this post, what's new about this information, how does it relate to what's been said before and how/why it matters.
Before hitting the send button, you, the blogger, need to ask yourself if what you've written can stand alone. Would someone who's finding your blog for the first time understand your latest entry? (Hint: if a reader needs to read all entries to understand your latest, you'll likely lose them.)