I did about two dives with my lobstering-expert-buddy before I caught one. After getting a lot of abuse from him, i was determined on the next dive to catch one. Came across a big one that had its claws sticking out of the hole pretty far. My plan -- grab both claws quickly from the top before it had a chance to move, then pull gently. One problem -- it was a softshell. I yanked the damn claws right out of him! My buddy was dying laughing and I was holding two claws, looking at him with the "what the hell do I do now" look on my face. I wound up putting the claws back into his hole, as if they were going to do him any good...
So I second the lesson (above) -- don't try to just grab the claws. I'd also add that you want to be quick and firm when grabbing the body, but not too firm. There's always a chance it's a softy and you don't want to crush him (whether he's a keeper or not!).