Duck is fantastic!
Crispy duck skin is absolutely heavenly.
Cook like mammal not bird, med rare is ideal, med is okay to if you are adverse to pink poultry.
Beyond medium, well...
Lightly score or thoroughly prick the skin and then salt.
Scoring or pricking allows fat to render out of the skin.
Don't go completely through the skin when scoring or pricking.
A little baking powder mixed in the salt will help crisp the skin when cooking
Air dry the skin at least 24 hours.
Skin must be dry to get a good trip to it.
Season any way you like.
Dry brine or inject brine into meat.
Several ways to cook.
Pan fry skin down to crisp skin, then finish in pan, oven, broiler or grill.
Grill skin down to crisp, careful! Very fatty, and can cause big flare ups and burn/ruin the skin.
Smoke then crisp skin by any of the above methods.
Those methods have all worked for me.
Again over open flame beware of flare ups.