Most arpeggios are tricky, mostly because of their shape on the guitar. If you find yourself working on blues or jazz, this is even more true; they take the use of arpeggios and broken chords very seriously!
Key is, just keep tryin'. Barres and partial barres will sound sloppy at first, like the notes are running together (like playing the bottom three notes of a minor chord, at the 5th fret). The only thing i can think of that may help other than alot of patience on your part is getting to know the mechanics of the hands and fingers. When I need to sweep a partial barre, for instance, I use a combination of palm muting and I roll my finger across the barre. Say, in an a minor barre chord, at the 5th fret: if you sweep upwards, beginning at the a on the highest-sounding string, you can actually lift part of your finger from the string as your pick proceeds to the next string. Does this make sense? This will help each note ring clear. On my way down, I use palm muting to make sure the notes don't ring too long, since I can't lift my finger in that direction:)
I hope this helps, but I admit it is kinda hard to describe.
Michael
