Step 1: Turn the Crab on Its Back to Begin
Take the hammer and lightly smack it around on the bottom shell between the legs and apron. Do not remove the apron or the hard top shell.
Step 2: Grab a Leg
Using your thumb as a pivot point, lever the legs toward you one by one and pull out the meat. If you have broken up the shell with the hammer, it should slip out easily.
Step 3: Repeat
Same as last step, different leg.
Step 4: Don't Forget the Lump That's Attached to the Large Claws.
Use the same technique to pull out the lump meat attached to the largest claws.
Step 5: Remove Remaining Shell
If the legs are too flimsy and break off without the meat coming out, just peel off the broken shell to get at the meat.
Step 6: The Remains
See, you've eaten all of the body meat without having once touched any guts or lungs/gills (whatever those gross feathery things are).