It's hard to just look at these and give an opinion on what you need help on. You have a beautful smile. More experience in front of the camera with additional photographers will help get you that experience.
Try not to lock your arms and feel more inside when posing or when directed into a pose. The brown shirt I think you just needed to turn more towards the camera instead of a profile body shot. Don't just stick your hand and hold it when placing your hand through the hair type posing. You have to feel it and act it. It will look to posed otherwise.
The outfit in number 1 with the fall background doesn't work so pay attention to fashion vs the scene. You have summer clothes and it looks like an early spring or late fall season.
Look at magazines, copy poses that work, crank up the music and pretend the mirror is the camera and practice. The best way to learn to pose.....