I hate to be that guy but if you can't come up with a topic of your own, or write about what interests you, you probably shouldn't blog.

Well yeah, I was gonna say that too.

Coding Horror blog has quite a few great articles on the subject of blogging - why, what, how, when to write, for whom etc.

Career choices for younger merchant sons in Venice in the Quattrocento.

Your bio says "Lives in Kolkata, India."

Anything about life in India as a developer, how the culture is different to western etc. Would be interesting.

Blog about stuff you know well and can share deeper insights into.

Thank you for this one!

Lisp macros, focusing not just on the resultant code but also the moment of realizing a macro'd be useful.

Things easier to do in a Perl one-liner than in an AWK one, and vice versa. (and maybe other languages)