When I was a boy, we used to get a bamboo pole and tie a string on the end and then tie a piece of bacon rind on the end of the string.
Bacon rind works very well because it is so tough that it does not dissolve in the water and the crayfish (crawdads in the South) cant tear it up.
We used to pull them out of farm ponds about as fast as you could take one off and get the line back in the water.
The most efficient way to get them however, is to seine them. Nevertheless, a seine will not work very well on a rocky bottom. But, if the bottom is smooth or sandy or muddy, you can pull out a whole seine full in one quick drag.
Just eat the tail. It is the only really meaty part, the cephalathorax contains nothing that you would most likely want and the meat in the claw is too little to be bothered with. Having said that, I have seen people boil them, pull the head off and suck out the contents of the cephalathorax. To each his own.
Bon apetite!