My choice to fulfill these criteria is self-hosted WordPress that is able to match all of these criteria through its extensive selection of plugins. The ideas themselves are universal and can be realized on multiple blogging platforms, but my examples on how to implement them are focused mostly on self-hosted WordPress.
1. Use your own internet domain
It is vital that you are in control of the domain for your blog. This cannot be emphasized too much! By controlling the domain, it is you, not the hosting company, that owns the traffic. This gives you the option to switch the host or platform, instead of letting the host own your blog.
Hosting your blog yourself, for example WordPress or Movable Type, is the obvious solution to this, although the hosted solutions Blogger and posterous allow you to use your own domain for free (you need to pay the domain provider, of course), hosted WordPress allows it for a fee, and it is included in the basic fee for Typepad.
2. Automatically promote your posts on search engines and social media
You want to promote your content, and search engines and social media are the keys to that right now. The services you want to post in vary depending on your audience, and considering the youth of the social media market, the big players may well change in the coming years.
For search engines, there is a WordPress plugin called Google XML Sitemaps, which creates and manages the XML sitemap for your blog and notifies search engines when it is updated.
For Twitter, a good WordPress plugin is WP to Twitter, which allows you to automatically tweet all your blog posts, and optionally customize the tweet when publishing a post. Another popular option is Twitter Tools.
For LinkedIn, there are two LinkedIn applications you can use to publish your blog: Blog Link (works with any blogging platform) and WordPress (for, you know, WordPress). You can also connect your Twitter account to LinkedIn and share your posts that way.
From there on, there are multiple options. For Facebook, there are multiple WordPress plugins available for publishing your posts (such as Facebook Page Publish), as well as Twitter integration similar to the application on LinkedIn. There are also external services, such as ping.fm and hellotxt.com that can be used to distribute your posts to a much wider range of social media, for example through posting them on Twitter first.
3. Provide multiple ways to subscribe to your blog
While many people may notice your posts from the messages you send to various social media sites, recurring readers will still want other ways to access your content to make sure they don’t miss anything in the hectic pace of social media. For these purposes, you want to provide an RSS feed and e-mail subscription.
4. Provide multiple ways for people to share your posts
There are lots of social media sites on the market at the moment, and your readers may be using any of them. In order to encourage them to share your content, you need to provide easy ways to share it to a variety of services.
There are lots of plugins available for sharing to a variety of social media. My current choice is AddThis, which provides excellent coverage and is available for any platform.
5. Provide an easy way for people to comment your posts
While the easiest way would be to allow unlimited, anonymous commenting, that is not an option because of spam. However, there are many ways to make commenting relatively easy for people.
The traditional solution is to include a check that verifies that the poster is not a bot. These checks, CAPTCHAs, come in two varieties, distorted images and questions that a bot is unable to recognize and answer. The distorted image variety includes reCAPTCHA and the question variety includes Block-spam-by-math.
Currently, this blog is running Disqus, which is a global comment system that connects conversations across the web. I am totally in love with this idea where the comments you make and discussions you have on multiple sites are aggregated in one place.
Another option, similar to Disqus, is Facebook comments. One of the WordPress plugins for implementing them is Facebook Comments for WordPress. If your audience is heavily on Facebook, this might be a good option, because it allows you to have the discussion both on your blog and on Facebook at the same time.
6. Show what is going on in social media on your blog
The full circle is completed by showing what is going on in social media on your blog site. Depending on your needs, you can, for example, show your own tweets (I use Twitter Widget Pro for this) or related tweets from Twitter or show your Facebook fan page and allow interaction directly from your blog (Facebook Like Box Widget).