I have built up my speed for picking at fast speeds by practicing for hours at a time, and finally a few years later, I as fast as James Hetfield, if not a little faster. Speedpicking starts with the wrist and ends with the wrist, no arms, u need to be relaxed, here is a simple tab to get u started.

0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0-0, these are done all with alternate picking, (going up and down)
now if u want to really build up speed, do a galloping pick

0-0-00-0-00-0-00-0-00-0-00, this riff is the type of riff metallica used in their song battery.
play these riffs slow, you will build up speed as you go. practice these as much as you can, and I assure you you will build up speed in your picking.
rock on all \m/