That's a tough one!
For me, the first step would be to define an overall topic for your blog. It doesn't have to be anything too narrow, but it's helpful for creating and managing your ideas. Once you have your central theme, start writing down what you'd like to know about it. For example, a blog with a central theme of "personal development" might have topics such as "managing your time", "creating better relationships" and "getting organised".
Using the list you've created, you can start organising things into categories. I wouldn't worry too much about these, as you can give articles multiple categories. It's best to create a more general set of categories. So instead of a category called "time management tips for at the computer", you could have "time management" and "Computer tips" and tag a post with both.
I wouldn't get too worried about categories being perfect. Just look at your blog for a reader's point of view, and ask yourself two questions: "What am I looking for?" and "How do I find it?" Make it as easy as possible for a visitor to answer those questions and you're all set.
As for the videos, I can't see why it would be a problem if you weren't in them. Having said that, it may help your readers to connect with you if they can put a face to the words.
Hope that helps
