Good question Mike.
First thing I'd say is that almost anything could be a suitable
blog topic. It doesn't have to be cutting edge or blindingly
original to be of interest to someone.
You could be writing about something you've been pondering, or a
new technique you've just discovered. The place where you are right
now, and the language you use, could be the perfect match for
dozens of other people out there thinking similar thoughts, or
trying to achieve similar things.
I'm living proof that just throwing out your ideas and thoughts as
they are is great for business. Web Design from Scratch gets in the
region of 5000 visitors each day, and provides the marketing needs
for our agency. The reason it works is that I published pretty much
everything I knew and thought about web design over a period of
time. I didn't do too much censoring or editing; I just wrote it
and threw it out there. Over 5 years, the content has been linked
to more and more, and has gained gravity for Google, to the point
that now it's a valuable marketing channel.
The most important thing is
JFDI. Start now, don't be too self-reflective, and
keep going. All content is beneficial, especially if you don't have
much yet.
Cheers,
Ben