a few tips and thoughts:
* the purpose of sweep picking is to articulate the most amount of notes with the smallest expenditure of energy. *There are some who would say they could alternate pick much faster than they could sweep, however,
alternate picking is a much heavier use of muscle.
* sweep picking centers primarily on coordination. *Yngwie Malmsteen has been quick to point out that he probably is not as fast as some might think, but the clarity of his picking creates the illusion of quickness.
* It is easiest to sweep pick with a very heavy pick. *The heavier the pick, the less energy you have to spend trying to articulate each string. *The idea here is to use just enough force to strum each string in succession.