I would suggest you write a few posts about the topics you feel you have the most to contribute. This will tell your readers what topics are in your wheelhouse.
For example, if you are doing something very technically innovative that I might want to integrate into my future projects, I'd want to read about it. If this isn't an area you are doing something cool, I don't want to read about the fact you are using Ruby.
I think the trick is to write about YOUR topic, and have that build into related posts as it would in casual conversation.
Given the infrequency of comments on most blogs, it may be hard to consistently add topics by responding to previous blog posts.
Heck... that's another potential topic: driving enough engagement to generate that back-and-forth. If it's a problem you have some marketing insight into... I desperately want to hear it.
The topics I think you "should cover for sure" are those where you have something interesting to say.