After years of playing and boat loads of techniques, I would say sweeping was the hardest for me to get down, and that is probably the case for a lot of people.

I actually had the problem of trying to learn the sweeps too fast. So I would kind of be doing it but it was sloppy, and I could never do it slowly.

I literally started all over and went as slow as possible. We are talking tediously, obnoxious slow. Assuming at least by now you have some typical major/minor sweep patterns memorized; One thing to try and do is to do the pattern with your left hand, without actually trying to pick it. No sense in trying to pick/sweep the strings if your not even comfortable with doing the patterns.

Once your comfortable with a pattern, try sweeping it but really really slow. having a metronome helps. Once your comfortable, go up 5-10 bpm. Its tedious and you need patience, but its very rewarding once you get it. Good luck!

Oh well I guess I should ask, what sort of music are you into? I can probably give you some tabs or something in the metal sort. I personally learned sweeping by playing Jason Becker songs insanely slow and gradually building up speed, I used powertabs to help me with that.