Ironically, I rank for many keywords that I'm not even targeting directly (though related to my niche) when I simply write longer articles and posts. This is a natural side effect of writing wiki style posts versus the shorter posts which are low on words and lower quality content. The more words you use in an article, the more likely you are to rank for any and all keywords targeted, plus ones not targeted. That represents free traffic you're not having to work for. My suggestion is just know your niche; write a lot and write often.