I play by ear so I won't attempt to explain anything to do with theory but I can sweep pick handy enough, just to add some tips to nailing the technical side:
1) type a double octave arpeggio up in midi, loop it, then play along at whatever speed you can manage - if you don't have a midi sequencer download Reaper for free or if that's not an option, play to a metronome
2) hold the plectrum the same way you do for alternate picking
3) play each note at the same rhythm - focus on the hammer ons and pull-offs making ure they maintain timing
4) lift the pressure on each fret immediatly after the note has been picked - helps maintain clarity
5) Learn to roll your pointing finger if it is barring a number of strings so that the pressure lifts from a note a soon as it is picked
6) practice the same arepeggio up and down untill you get it, then practice running up with one arpeggio and down with another
7) use the neck pickup when you start and reduce the gain on your amp - when you think you have the technique down then try it off the bridge (you will find this a lot more difficult if you have high output/hot pickups!)
8) when you are picking a sweep run use the thumb of the picking hand to mute as well as the ridge of the hand - very important if you want to be able to play cleanly without having notes ringing out all over the place.
9) once you know the shape you want to play and can do the left hand movement, spend some time visualising the technique. Because it is very different to regular alt picking a lot of guitarists find it very difficult to get their brain to accept the simple movement generating the difficult sound. Think about it, visualise it and understand the movement and you will find it 100% easier to do. The biggest difficulty in sweep picking is getting the penny to drop in your mind.
Hope this helps!