It's really not as hard as it seems. With an Iphone or another sort of cell phone, you just want to make sure you're not super close to the subject so that your phone can't focus. Try to keep your hands steady, and don't be afraid to take multiple of one pose or position. Whenever I take pictures of something, I always take extra and I usually get half of them as really good and the rest are unsatisfactory.
Also, don't be afraid to angle your phone a little bit when you're doing poses, it can add a lot of emotion and movement to your photo.
Another thing that really helped me was experimenting with things, whether it be different lighting, what angle you're taking pictures from, your background, etc etc. You probably want a white or other light, neutral background (A light grey would work just as well) and you don't want anything too distracting either.
All it really comes down to is experimenting to see what personal techniques you develop. Some stuff I've come to adopt as personal techniques include angling my camera for almost every shot, leaving the depth of field really low so that only a small portion of the photo is in focus, etc etc. (Of course, for mocs you want as much in focus as possible)
Hopefully some of this makes sense and helps!