The essence of a great photo is capturing a moment within the constraints of a rectangular frame. Taking note of the elements in the picture and composing them can lead to much better photos. Try not to merely snap the shutter, but take a good look and examine what is in the frame. Is the background clean, or is it quite busy? Are there objects growing out of your subjects head?
The background is clean and explains where the subject
is while not being distracting.
While centering the image on your main element may by your gut reaction, photos shot like this tend to feel artificial. Try to align your subject off to one side, by imagining the image is split into thirds and forcing the subject into one of the outer slices, achieving a more natural look.
Placing the subject to the far right third of the frame,
as in this photo, is more visually interesting than had the subject been centered.
Finally, let the main element fill the frame. Capturing your friends full body into the picture will leave you squinting to see their face, cut out the unnecessary elements and get in close.
The subject's face takes a sizable portion of the photo,
while still showing where he is.