I've found a technique for wrapping peacock herl that is probably known to everybody but me.
Just as you can use the supported tag end of your thread to provide nice tightly spaced wraps of your thread base as you wrap down along the hook shank I use the same method of using the same thread tag to guide wraps of herl. This gives me a very smooth herl body with no overlaps. I also seems to "encourage" the barbules on the herl to all stand up as neat as can be and not wrap each other down. I'm amazed at how nice the bodies look.