I find that the easiest way for me is to tie them upside down from a tree branch by their feet- they will calm down immediately. Tie their wings around their body with twine as well. Then tie a rope around the neck. Quickly hold the rope tight with one hand and cut the neck with one swift stroke. Make sure your knife is super sharp. If the wings are tied there should be very minimal movement after decapitation. Other ways like with a killing cone are good, but I would always tie the wings. This way works with roosters up to about 10 pounds at least.