John Petrucci gives some great advice on his 'Rock Discipline' DVD about sweep picking and all speed related techniques. As does my teacher Tom Hess...

http://www.tomhess.net/

When I teach I always get people to master techniques slowly first then build up gradually. It helps to build up accuracy, strength and most importently confidence. Work with a metronome to a plan over a few weeks or months and you'll really start noticing great results.