start as slow as humanly possible. Make sure each note is being hit clean and steady, before you move on to the next. Do it so slow that it bugs you to death, then faster and faster, as your coordination between each hand synchronizes.

I started by switching between 5 and 3 stringers, simply for songwriting purposes, then i started doing 6 and 4 stringers. make sure your transitions from one sweep to another are as clean as each note hit, obviously.

if you want a great example and good explanations, then check out everything that The Jonezter put on here, cause he is quite proficient in the sweeping area.