I know most will think this is not worth mentioning. However, I have seen many tutorial videos in which stacked hair is removed with the wrong hand. Even a video I watched by Davie McPhail did it "wrong". In that video, he, and many others, remove the hair and then switch hands. This tends to defeat the purpose of stacking as the tips often misalign in this changing of the hands.
If one is tying a forward tip hair fly, such as the comparadun family of flies, the hair should be removed with the right hand. The stacker should be held in the left hand.
If one is tying a rear facing tip hair fly, such as the caddis family of flies, the hair should be removed with the left hand. The stacker should be held in the right hand.
I hope I explained this reasonably well. It is just that I see all these folks carefully aligning the tips of hair and then switching hands before laying on the hook, thus messing up the tips again.
At least, that's my opinion.
For a Comparadun/Sparkle Dun:
For a Caddis Fly: