In the visual arts — in particular painting, graphic design, photography and sculpture — composition is the placement or arrangement of visual elements or ingredients in a work of art, as distinct from the subject of a work. It can also be thought of as the organization of the elements of art according to the principles of art. - Wikipedia (click link for more details)One way to help achieve this in any photo is by cropping photos appropriately. One rule of thumb to keep in mind is to avoid cutting off limbs in awkward places. Cutting off feet is something I commonly see made with a lot of good photographers on the grid. If you have to crop off at the legs, I recommend hitting about mid calf or mid thigh. Same applies with arms - don't cut off right at the elbows - hit mid forearm or bicep.
Keep in mind the focus of the photo. Whether it be landscape, model, fashion, object or shoe - make sure that you don't have so much going on that the photo loses the subject.
My biggest suggestion is to play. Following I'm showing an example of playing with different crops all from the same photo.
Two-thirds Body Crop:
You see that even playing with the dimensions causes your eye to look at different elements but all maintaining the focus, which in this case should be the model.
Dress: Mon Tissu
Skin: Tres Blah
Pose: LAP aka Long Awkward Pose