Step1
Set up. This project is best done outdoors as it can get messy. Have your ice chest of crabs, gut bucket, hose and a tray to hold the crab after cleaning near at hand. If you are doing more than about 6 crabs, find a lawnchair so you can sit comfortably. You will also need some sort of hard solid object or surface for whacking the shells, I like to use a cinder block or a corner of a heavy picnic table.
Step2
Get the water started. Fill your pot about 3/4 full of water and set to boil. You will need to add salt to the water. Take it from the marine biologist, if you cook a crab in fresh water, the meat will be mushy and gross. I try to mimic the ocean's salinity as close as possible, approximately 35 parts per thousand. Simply multiply how many cups of water you are boiling by .035 to figure out how many cups of salt to add. Add your flavorings.
Step3
Now its time to start cleaning the crabs. You can drop a live crab in a bucket of fresh water to "anesthetize" it, about 10 minutes. Be careful not to leave them in fresh water too long or they will die and you should NEVER eat a crab that has died before you cook it!
With the crab sitting belly down, place each hand around a pincer arm and pull them back out of the way so the crab's face is exposed. Get a good grip on the body, but don't put too much pressure on the legs or they break off, you just need to keep them out of the way
Step4
The strike point is the crab's "chin", where the mouthparts meet the shell on the underside. Give it a good hard whack against the solid object, hard enough to break the mouthparts and stun the crab, but not so hard that you totally smash it.
Step5
Quickly remove the shell by pulling in a sideways-upward motion. Grab the left side of the shell, pull up til it pops free, then pull sideways to the right. Your crab is now dead because you have essentially removed and/or severed the central nervous system. If steps 4 & 5 are done in rapid succession, the crab will never feel a thing.
Step6
Remove the apron, or tail. The apron is a triangular shaped piece on the belly of male crabs (females have a wider, more spade or apron-like shape). You will see it is jointed. Press your finger on the second joint to make the first one flip up so you can get ahold of it. Carefully peel it all the way back, it should break off at the base of the shell leaving a clean channel into the gut cavity. Be especially careful of the male's reproductive parts inside the apron, they are needle sharp and are very painful to be stabbed with.
Step7
Pluck off the mouthparts, shake the guts out into the bucket (removing the apron first makes this easier) and remove the row of gills on each side. Gently snap in half down the center channel, you can fit more crabs in the pot if they are halved.
Step8
Repeat steps 3 thru 6 for each crab until you have enough to fill your pot. If you have more crabs than your pot will hold, leave them alive until you're ready to start another batch. Using the hose and spray nozzle, clean out any remaining guts, sand, mud, etc...Shake gently to get rid of excess water. You should end up with a tray of nice clean crab halves.
Step9
By now your pot of water should be boiling nicely. Carefully add the crab. When the water comes back to a boil, time it for 16-18 mins. STAND GUARD. You may have to adjust the heat, you want it to boil, but not boil over.
Step10
When its time for the crab to come out, I will usually rinse them again to remove any chunks, foam, pieces of lemon, etc. DON'T just douse or soak in cold water. Remember, fresh water is a crab's worst enemy. I take a half in tongs and rinse JUST the legs, keeping the water away from the body meat.
Melt some butter and dig in, you've just created a meal fit for a king!
Novice 
