I've found a good way to learn/practice sweep picking

[JDC]

I was just practising my sweep picking and discovered a good way to make my down strokes more consistent

basically make a chord, I prefer one such as 4th string 12th fret, 3rd string 11, 2nd string 10, 1st string 9 (aka Major 7th chord)

you keep the chord fretted and do down strokes using the palm to mute the strings so each rings separately but keep all the notes fretted!

your basically trying mute them at the right time with the palm, too early and you'll kill the note and it won't ring, too late and the notes ring out together


extra tips
I  don't really pick the string, you more kind of "nudge" it with the pick, and usually using the arm instead of the wrist (although herman li does it from the wrist but he probably mutes it slightly differently)

and use the neck pickup! (it's easier to keep clean) and try playing around with the position where your palm mutes the string

[silentrage]

i was told by someone who's pretty insane with clean sweeping that you need to mute with your fretting hand and not picking hand.

[Oli]

With sweeping, you really need to release each note with your fretting hand, so you only have one note fretted at a time. Using a combination of your fretting and picking hands, you mute the strings that aren't being swept at that point.

If you chord the notes, and jute palm mute, you'll get a kinda rake sound, which could be desirable, but it's not as clean as a sweep :)