Something Different? - SEO approach

I've been doing mountains of research on SEO and while still new, I think I have a semi-firm grasp of 'best practices'. Unfortunately, some SEO approaches don't really apply to my site/market, and could in fact, hurt it. Which leads me to my question...

My site is 100% pure content. I sell absolutely nothing on my site. Money is made through a standard adsense account. The content and writing is unique (not stolen or plagiarized) and of high quality. My problem is, that the content wildy varies on topic/subject. One article might be about particle physics and the next might be about gummy bears.

Most of my organic searches are for the individual pages that they're about. I rank well on some, and not so well on others. Key words being searched also wildly vary but they do get me hits. (traffic has been increasing)

I could try to focus on a few single keywords, but the keywords involved would have to be very, very broad. Like 'Science' and it would be far beyond my ability to rank with words that broad and competitive.

So other than the standard SEO practices, is there anything else I should be doing? Is there anything I can do that normally wouldn't work well with an e-commerce site, but work well with mine?
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