I prefer cooking crabs by boiling them in a big pot halfway filled with water and with a few tablespoons of salt. My son prefers steaming them in a metal steamer with just enough water.
Before you put your crabs in the pot, your water should be boiling high. Dunk each live crab (head first or where the mouth is) one by one, holding it with a tong, or with your hand covered with a thick kitchen glove. If I use the tong, I hold the crab in the middle portion of the crab gripping as hard as I can so it doesn't slip.
Sometimes the crab fights back and that's when I get my thick glove and hold the crab in one of it's smallest claw and I quickly dunk it into the boiling water. Cooking time should only be about 15 to 20 minutes. Crabs should be fully submerged in water when cooking. Crabs should all turn red when cooked.
When cooked, let rest for about 5 minutes. I always serve my crabs after cooking. So get one crab, lay it on a cutting board and remove the white covering underneath. Open the crab separating the red shell from the other white part that contains all the meat. Clean the shell by removing the part in between the eyes which is the intestine. Leave the red fat which is the best part of a crab. Chop or cut with a kitchen scissors the tips of all the legs. Next, cut the other white half part of the crab into two at the center. Crack the claws and the legs with a kitchen mallet or the back of a cleaver to make them easier to eat. To avoid splattering on my kitchen, I put my crab inside a big Ziploc and then I pound with a mallet. Then cut each of the two parts into three with their legs still connected. Do the same to all the crabs. Serve all cut parts on a big platter and top with the red shells. Serve with lemon-butter sauce, cocktail sauce, or vinegar & oil, or you can make your own. I like mine with coconut vinegar with chopped yellow onions, salt, and with a drizzle of sesame oil.