Lest everyone get the idea the only subjects I shoot are landscapes and urban environments I do portraiture as well on occasion with the Friends of Bill Project.
Say you have a friend or family member for that matter shove a smart phone or a camera into your hands and want you take their picture, here are some great tips. Understand what your camera can and cannot do, doesn't matter if it's a iPhone or Android handset or a Nikon D4, it's the person using the device that makes the photo.
First off understand the rule of thirds, if you are shooting horizontally or in landscape, you don't want your subject's head smack in the middle, I usually shoot slightly off centre. The second thing you want to do is make sure your subject's eyes are sharp, this is more the case with a proper camera than with a smart phone. Finally you want to make the light work for you, contrary to popular opinion overcast days have great light for portraiture as the light is diffused, the same goes if you are going to be in the shade as the case with my friend Lindsay on the bottom.
Now also bear mind with photography, rules are meant to be broken as I did with my friend Dave, the light is bright, almost harsh with lots of shadow being cast and that was used to my advantage. Granted this wasn't Dave's favourite portrait of himself as he was suffering jet lag from just flying in from the UK to visit family. He doesn't like it, I do so there.