Whiskey Creek (http://wcflies.com/blog/) is an excellent blog site on how to tie. It has many outstanding examples. I enjoyed this p0st re peacock and to be honest, I have often purchased strung peacock and tied herls in by the butt only to be disappointed with the smothering of herl fibers. I often find the tips too fragile on the cheaper herl. Here, Whiskey Creek gives great advice on one of the most important fly tying materials. 

Whiskey Creek FF
Whiskey Creek FF

“Compare the herl coming from the eye and from a string. Notice how the eye herl has even fuzz on both sides of the stem. For the strung herl, one side is better than the other. For strung herl, its best to twist it into a rope, so that the best sides come forward. The eye herl is on top, strung on the bottom (but you could tell that already). ”

Mark this site for excellent info, especially re wet fly construction.