For a long time, I tried to use my blog as
SEO fodder (years ago) and while sometimes it worked and sometimes it didn't, it never brought quality traffic.
Then, I gave up on all that and simply decided to write when I felt like it. That turned out to be never. Heh. Not terribly successful that.
Then I started writing at least once a week on things that I not only knew about, but could speak well on the subject.
And that's when the quality traffic started rolling in.
My favourite (and most popular) post was pretty much just a rant, but to date is still in the Top 3 globally as a "how to do XX properly" (not into shamelessly self-promoting here any more).
So yeah, I consider that an overwhelming success, given that it was a rant, it got the point across, it brings in buckets of traffic, and occasionally some of those folks convert into paying clients.
I suppose for reference, my advice would be to write in Your Voice about What You Know. The latter'll get you Googled, the former'll get you business.