^^
This. I'm from Southern MD. Work in a crab house and these instructions are good enough. Key is STEAM, not BOIL. Old Bay or JO spice. Cider Vinegar (no butter). Don't clean before cooking. Just drop in the steamer (already steaming) and wait, make sure they are alive before cooking. Use a basket or false bottom. Boiled crabs are mushy, flavorless and hard to pick. Any other way is blasphemy (equivalent to crockpot ribs) and might get you shot in some parts (j/k). Get some good corn and saltines.
It is supposed to be messy.
http://www.oldbay.com/Recipes/Crab/Main-Course/OLD-BAY-Steamed-Blue-Crabs
How to Steam Blue Crabs Maryland Style - YouTube
I don't ice them if you are eating them shortly. Don't store live crabs in fridge or closed cooler. There won't be enough fresh air and they will suffocate. Just put in basket and cover w/ cold damp towel, or leave lid open on cooler.