Nobody wants to start a blog only to run out of ideas three weeks later.
If you're thinking of starting a blog, here's an easy test to help you decide if your subject area will keep you engaged over the long term: Sit down with a pen and a blank sheet of paper, and start writing down titles for blog posts. Just titles. Don't stop until you've written down every title idea you can think of.
If you can come up with forty or fifty decent title ideas with relatively little effort, then you have a truly sustainable subject.
You can transform this list of titles into a surprisingly large store of content by using the essay test technique: Set a timer (10-15 minutes per post is usually a good length), and pound out a quick, unedited first draft of a post. When the timer goes off, move on to the next title.
Do this for 1-2 hours per day, working systematically and relentlessly through your list of titles. In a matter of just a week or two you'll generate a massive amount of usable first-draft content.