First, a quick clarification of 'successful'. In this instance, I mean a blog post that receives a large number of page views. For my, little blog the most successful post ever got almost 57,000 page views. Not a lot by some other standards, but I was pretty happy about it.
Looking at the top 10 blog posts (by page views) on my site, I've tried to distill some wisdom about what made them successful. Your blog posting mileage may vary.
1. Avoid using the passive voice
The Microsoft Word grammar checker has probably been telling you this for years, but the passive voice excludes the people involved in your blog post. And that includes you, the author, and the reader. By using personal pronouns like I, you and we, you will include the reader in your blog post. When I first started this blog I avoid using "I" because I thought I was being narcissistic. But we all like to read about other people, people help anchor a story in reality. Without people your blog post will sound like a scientific paper.
2. Engage the imagination of your readers
You need to draw your reader into your post. There are two good ways to do this: stories and firing their imagination. People like stories, narrative keeps them interested in knowing what happens next. But firing the imagination is even more powerful: if people can start imagining themselves in the situation, or how they would solve the problem the blog post is talking about they become more fascinated.
I put down the success of More fun with toys: the Ikea LILLABO Train Set to the fact that the problem being described is easy to understand, and people could instantly wonder how they'd solve the problem I was describing. Double checking Dawkins did well because it's a detective story.
3. Spend offline time thinking about the post
Most of my blog posts are written in my head. I'll lie in bed at night or sit on the bus in the morning and repeat over and over again in my head the sentences and paragraphs I want to write. By head writing I listen to my own words and make the readable. And this head writing let's my imagination run riot. This sort of brainstorming leads to lots of new ideas that can be incorporated, and it avoids the fearsome blank page problem where writer's block can begin.
If you want to do one thing to make your blog posts better do this: walk away from your computer and stare out of the window.
4. Write and write and write
When I began this blog I didn't know what to write, and I thought I only had a few ideas. I ended up writing short, boring blog posts and saving my ideas up because I was afraid that I would run out of things to say. It turns out that the opposite is true. The more you write, the better you get at it. And the more you write the more ideas seem to appear from the ether. I don't set myself a goal of a blog post per day, but I do try to prevent my blog from going stale. Some of my posts are winners, some are not. But I would not have written successful posts without having written the duds.
I never would have written How to sleep on a long haul flight if I hadn't already trained myself to write. The topic seems rather dry, but once you start imagining writing about something you can, if you've got into the habit, tease out the interesting elements of the subject.
5. Avoid blog posts that are reposts of other people's material
You know those blog posts where someone grabs the initial paragraph from someone else's blog post? They publish the paragraph, comment on it, and then link to the original. That's boring. They haven't added anything significant.
If you want to post about someone else's content then add something significant: if you can't add something significant then what you planned to say is likely better written as a comment on the original site. I have commented on other posts in the past; for example, in A bad workman blames his tools I wrote a riposte to a post I strongly disagreed with.
6. Reread your blog posts aloud
I find that the only way to improve my writing is to stare at what I've written and read it aloud. Suddenly, when spoken, awkward phrases become apparent, the places where the flow ebbs become clear and repeated use of certain fetish phrases (I over use 'In fact') stand out. If you can't actually read aloud because the people on the bus (or wherever) would think you strange, then read aloud in your head: deliberately and slowly enunciate the words in your head.
I read and reread sentences and paragraphs over and over again. Each sentence in one of my blog post has likely been read four or five times before I hit publish.
7. Be playful and create something new
Commentary can be interesting, but what's often more interesting is new stuff. This means you actually have to create something: the blog post will just be a description of what you did. Some of my most successful posts have been about things I've done. For example, lots of people read about my attempt to 'hack' a spot-the-ball competition in Tonight, I'm going to write myself an Aston Martin. That blog post required a lot of work before any writing began.
You need to be playful away from your blog (and, perhaps, your computer) to come up with the sort of posts that will be winners. Walk away from your blogging software and think about something else. That something else might make a great post.
If you can find a subject that can be taught in the space of a blog post then do it. People won't read blog posts for long (the average person spends about 3 minutes on a single blog post on my blog), so you need something bite-sized and interesting. In Squaring two-digit numbers in your head I showed people an arithmetic trick and told a little story.
9. Be personal
I said above that I'd avoided "I" in the beginning. This was a big mistake. You need to speak from your heart to come across as genuine and interesting (unless you are an excellent writer), oftentimes this means speaking about yourself and about a subject that you are passionate about. In Just give me a simple CPU and a few I/O ports I wrote about my desire for a simple computer and how things had changed over the years. The post doesn't have a lot of insightful points, it's really a personal story.