Browsing around Phillip J. Eby's blog, I noticed that his first post summed up the best approach to starting a blog. What you start with is not what you want it to be. So, don't wait to figure out exactly what you will talk about, how the site will look etc, just start with something. You rarely know what you want (or don't want) until you have some kind of experience.
I have seen plenty of starter advice suggesting much planning and consideration, and this is very valid if you already have experience or a concept. But if you don't, then don't wait for it to happen.
It looks like Phillip has quite a few interesting thoughts on the site, so I'll be spending some time reading there. Thanks Phillip.