First of all, it ain't easy...so don't get down about it. I'm not sure I understand what you were told about how to do it, but I can say that I've heard better advice on the subject. I know some of the guys here have posted lesson snippets about sweeping technique and exercises, so search the forums here and at http://www.racerxband.com/forums
. Specifically the Guitarist forum at racerxband.com.
The one thing I can tell you that helps me out more than anything else is start SLOWLY and work up, even after you become proficient at it. Speed is important, but hitting every note cleanly is more important. And use a metronome. There is NO substitute!!!