I think that it's pretty much a scientific fact that fish love crayfish. Be it bass to carp to catfish to big ol' trout, fish slurp up crayfish with something close to reckless abandon. It only makes sense to have a crawdad in your arsenal.
With that being said, here is my simple to tie pattern, the Big Daddy Crayfish.
I've heard that fish will hit a crayfish that has undersized claws more readily that one with fully developed claws. If that is true or not, I honestly don't know. So I try to stay on the line of average claw size, maybe slightly smaller.
You could also add some barbell weights just at the hook bend, but I've found it a bit difficult to do with the claws in the same spot and the thread buildup from making the claws, so I normally just omit that.
Big Daddy Crayfish
Claws: Brown Bucktail
Body: Rust colored dubbing
Legs: Black Saddle Hackle
Shell: Orange Mottled Thin Skin