The best thing about shooting location portraits? You have plenty of control. If you don't like your subject's outfit, put it in shadow. Subject in a grumpy mood? Try a glass of chardonnay. Smile resembles a scowl? Go for a backlit silhouette.
Oddly enough, though, when it comes to backgrounds for location portraits, many photographers throw up their hands and relinquish control. Often, they shoot where they find their subjects, against cluttered backdrops that, at best, contribute nothing, and, at worst, actively distract from the subject.