Make it easy for your readers.
The best way to do that is to write like you talk, not like you write.
Be conversational - let your personality come through! That's so important.
Remember that your blog is not a scholarly essay, please! Here's a key point: if you write for your readers, your SEO will just happen naturally.
If you always have your topic in mind, and you always have your readers in mind, how can you help but use your keywords? If your topic is ultra-specific, you can't help but make it keyword rich.
Your posts don't have to be long, but make them long enough to discuss your point and deliver relevant content.
Relevance is manna to your readers as well as to the search engines.
Blogs are not scholarly essays.
They are not reports.
They are not white papers.
They do convey information but if you want avid readers, convey that information in an entertaining, conversational way.
Let your readers get to know you by having a conversation with them.
Ask questions - also a good way to get comments.
Before you start to write, get a mental picture of your reader.
Talk TO him, not at him.
After you've written your post, read it out loud to be sure it makes sense.
Check your spelling! If you want to be seen as an authority, make sure you spell words properly.
Grammar and punctuation aren't as critical, but make sure your post is readable.
Incorrect grammar and punctuation can make it confusing.
Make your blog interactive.
Interactive? Yes - if your reader has something to do he will be more likely to stay this time AND come back later.
Put up a survey or a poll.
Make him know that you value his opinion.
Don't forget to ask him to sign up for your feed or newsletter.
If you want him to do something, you must tell him what you want him to do.
Pay attention but keep it light.