I have a video and TAB for a good Double Thumbing warm up here-
http://jasperlamb.googlepages.com/do...warmupexercise
This exercise is designed to limber up the hands so that you can play double thumping lines at speed and have good, solid, even notes. It only goes for 36 seconds, but I find this is enough to loosen things up and help lose the stiffness that can lead to slightly ragged timing.
