I bent Archie Fisher's ear about this at the Chester festival sometime in the 80s.I had no problems playing arpeggios but the alternating thumb eluded me. He recommended going into a dropped D tuning which I did and found that it gave a real meaty effect.
   Many years further down the line I,ve come to find, after meeting many different guitarists, that people use whatever methods they find most comfortable and it helps to be flexible.Many players anchor the little finger to the guitar but this feels uncomfortable to me but 1 rule I do tend to follow is that my thumb plays the bass strings E,A & D,my first finger plays the G, my middle finger the B and my ring finger the top E.
   Meeting other players and talking and playing with them is a great way to pick up tips and I sometimes wish I'd done it sooner than I did.
   One last thing, practice, practice and then practice some more
   
Good luck with it and don't give in. You may come up against obstacles but persevere and you'll find your own way round them.
Cheers
Willow