It is difficult to create a composition when you are panning. Usually you end up with only the subject sharp and then not much of interest in the rest of the picture. Try to choose a background that will add value.
In this shot I was following the girl with a shutter spped of approx. 1/30 seconds, as her friend slowed down to hang on to the bike. She is sharp and he is semi sharp. As he is moving - but not as fast as her.
The two people in the background are completeley blurred as they were sitting stil.