My first step is to stumble across a topic I think others may find interesting. Then I just start writing. The first pass generally comes out as a bunch of poorly organized random thoughts, but once that process is done I tend to have a much clearer idea of how I want to present the topic.
From there I can rearrange what I've already written, which is usually ~50% of the content, and fill in the rest. I will revise the post until I feel like it is coherent but I don't get too hung up on getting it perfect.
I started blogging back in the Fall so I'm just forming the blogging-habit but I'm finding this method works well for me. It removes the writers block problems I've experienced in the past and makes the process much more enjoyable.