Being clear and having a direction for the content you are going to publish is they key to creating a consistent and valuable blog.

First of all write down all of the topics you are interested in. After that group the topics into the group of two: you're competent in and ones you are just interested to. The ones that you are expert in should be your core categories in your blog. My example: I started out as a designer, doing Photoshop tutorials and focusing more into web design. I didn't write about the icon design even though I was always fascinated by these beautiful creations.

For the Despreneur I have created a long list of the keywords and topics I had experience and was interested in. After that I have boiled it down to core categories that wrapped up these smaller topics. You can see the final categories at the top of the site.