After a while in the "biz" you get a sense of what is good and what is not. I think it took me a good six months or so of consistent
SEO writing before I found my groove and intuitively understood what was wanted. You start to figure out what info is gold in your research and what is crap ... Also, if you go about writing articles by asking yourself "What would I want to know about this if I was a consumer," you can typically turn out a good article.