Lateral or Horizontal picking?
On Single string runs then you want to concentrate on having the smallest possable pick movement, start of really slow with a metronome and gradually build up speed.
Play in 16ths (4 nothes per click) and accent the first note on every click this will help you build up pick control rather than an uncontrolled spasm.
Then start adding notes in, chromatically is a good place to start, then diatonically.
For across string chops my absolute favourite exercise is the Sailors Horn Pipe Jig, has everything you need, alternate picking, economy picking, intervalic picking and string skipping.
If you can affoard it John Petrucci's Rock Discipline DVD is pretty much the bible of melodic shread.
If not try
http://www.shredaholic.com for some great shread lessons or
http://www.wholenote.com for a really detailed site on guitar playing in genral.
One last thing, if you don't have a metronome, get one, it's one of the most important peices of equipment you'l own (although it does have a tendancy to drive people insane).