Robin Rendle was asked for career advice, and he said to take care of your blog.

While that's not great direct career advice, as either general advice or meta-advice it does seem sound.

As general advice, it's great because no matter how or what you blog, it offers a chance to practice rationalizing your thoughts with few constraints. Maybe you treat it as a journal, in the computer-science sense of a scratchpad where you work out and condense putative changes to a work, before they are committed to. ¹ Or maybe it's a accessible repository of notes where any worthy book read then gets a summary and is dumped into an entry with the quotes that have reasonable odds of being recalled in the future. ²

As meta-career-advice, blogs are similar to careers in that you start them with just a hope of where they will eventually lead. And it's up to you to keep working at them to make them into something that you want.

Of course, your blog isn't good for anything unless you actually begin. So just start writing, and trust that you will figure out what it's good for in some not-so-distant future.