Sometimes I just let it sit on the bottom and sometimes I give it a long slow strip or even a small twitch. I pay attention to the fish's reaction and the fish tells me how to move the crab.
If I put the fly in front of the permit and let it drop to the bottom and he doesn't show any interest, I might give it a twitch to draw the attention of the fish to the fly hoping for a take. I've noticed when fishing for permit: a technique that worked on one may not work on another permit. Each fish reacts differently for the most part....go off the reaction of the fish to determine how to fish the fly.