A quick google search gives you plenty of guides, telling you how to compose good blog posts (1, 2, 3 examples). So, why this one? Well, everyone has her/his own ideas about this.

Paul Foreman for mindmapinspiration.com

Here is mine.

• Write personal posts. Have your own opinion and stand to it. You don't have to be objective. Weighting arguments, however, makes posts ever more interesting.
• Write what and how you like to read.
• Use lists.
• Set links to resources.
• Less is more. Don't write thousands of words to cover a whole topic. Bigger issues can be broken up into smaller pieces. That makes reading easier. To establish coherence, the posts can be linked to each other.
• Use pictures, videos and other visual means as often as  possible.
• Give credit, if you use other persons' content.
• Use post splitters to keep your homepage tidy.
• Update your own posts, but make these updates visible. So, don't delete a sentence, but strike it through, and write new sentences bold face.
• Do not re-blog. You can have a twitter account and show the tweets in your blog. Here, you can make your readers aware of an older post that becomes actual.