I've always thought that one of the more deadlier sins was to take badly composed photos of your friends.
Like this one:
There's clearly way to much going on in the photo. And even though the guy's probably thinking "here I am in my best 'I'm really serrious' pose", the photagrapher makes nothing of it. The picture is cluttred with people and goings-on.
Compare the above to this one:
A real classic photo of Malcolm X. Note that the 'I'm really serrious' pose' is the same. But this photo captures everything interesting and doesn't distract the viewer with any other stuff.