Try never to freeze your crayfish. There is a big difference in taste between frozen and fresh crayfish. If you really must freeze it then break the tails from the body and freeze seperatly. And never ever freeze cooked crayfish. It taste like cardboard.
Live crayfish can be drowned in fresh water. Or by piercing the head with a sharp spike.
To cook them you can weigh it and cook it 6 minutes for every 500 grams.Get your water boiling, add the crayfish and when the water gets back to boiling you start to time it.
After cooking it the shell must be scrubbed clean and your crayfish is ready to serve.
Remember to remove the alimentary canal.