You're absolutely correct to be thinking about SEO, beyond just writing for your audience. I've managed to have some viral posts, but I also get big successes from SEO.
I think these two things are the most important:
1) Have a keyphrase in mind from the beginning, around which to focus the post. Research this, if possible, with the Google Keyword Tool.
2) Monitor Search Analytics to identify opportunities you haven't thought of.
For example, when Google introduced their new logo, I immediately started writing a blog post about it. There was no keyword information available yet, but I figured people would be searching for "new google logo." So, I optimized my post for that.
A few days went by, and I noticed that I wasn't ranking that high for "new google logo." There was lots of competition for this from highly-reputable sites.
BUT, I discovered by looking at Search Analytics, that I was doing pretty well with "google logo font," even though I hadn't optimized for that. Specifically, people were searching for "what font is the new Google logo?"
So, I optimized my post for that (I changed the URL to end with "googles-new-logo-font"), and even fleshed it out a little more to talk more about the font being used in Google's logo. I also changed the title of the post to "what font is the new Google logo?" (notice that I'm still hanging onto hope that I can have a ranking for "google's NEW logo," which may not be the most sound strategy.)
Now, I rank really high for "google logo font," and it is consistently bringing in new email sign-ups.
I've used SEO to entirely fuel 5-figure-a-month passive revenue businesses, and rely in it heavily for building my audience. (I'm not very good at paid traffic, but I'm good at free traffic.) So, if you want to know more, feel free to set up a call.