ok here is how...
First of all remember :
when playing two notes in one string do the alternate picking and when "sweeping" one note per string.. just keep "picking" up or down.
Then:
STEP 1: You can build a diagram with all the notes of the triad, and all the triads of the Major Scale.... (to bagin just do this on two strings: first and second)
Let´s say C Major, that´ll be:
C Major Triad
D minor triad
E minor triad
F major triad
Gmajor triad
A minor triad
B dim triad
(and so on)
STEP 2:With a metronome start playing this very slowly(and remember the tecquine tip I gave, pay your Most attention to this) then you ca gradually speed up.
OK-- You have just started... Then you can "add" another string (only one note in this string) so there wouldn´t be triad, but short "sweeps" BUT IMPORTANT keep including JUST TRIADS NOTES (from the triads I have just mentioned)
Repeat STEP 2
Ok... after finishing you 6 string sweeps you can start including 7th, 4th, 9th, what ever you wish.. Just remberber the first tip and never forget to start slowly with a metronome paying attention to your tecnique.
Also remember sweeps are based on triad, which also are the base of chord,... sweeps are chords displayed one note per string.. So you can reproduce ANY scale, ANY chord, Any harmony...Just keep this mechanism and you will succeed.. ONLY YOUR MIND IS YOUR LIMITATION!!!
PS: hope my explanation was clear,.. PM me if you have any doubts