I always see people doing the typical swing a 5lb plate around in circles as a half-whit warm up for the upper body. One of major objectives of the warm up is to activate the muscles needed for correct movement (which usually happen to be smaller ancillary/fixator muscles) and work on the ROM. Below is a very easy way to accomplish this without much space or equipment.
[video=youtube_share;AnouoFmrzsY]http://youtu.be/AnouoFmrzsY[/video]
[video=youtube_share;AnouoFmrzsY]http://youtu.be/AnouoFmrzsY[/video]