Pull off the head if it is still attached. Peel off the outer shell. It's easier to peel from the 3rd segment from the head. In this recipe, I'll keep the last segment of the shell and the tail tip on (which is how we make shrimp tempura).
Devein the back of shrimp with a skewer. The vein runs right along the back. Insert the tip of the skewer sideways about ½ inch (1.3cm) down from the head of the shrimp and pull the skewer tip up towards you. This will lift up the vein and you can pull off the vein with the skewer or with your hand. If the vein is broken, then insert again a bit lower towards the tail. If you can’t find the vein, then don’t worry about it. You can still devein the same way even with the shell on prawn.
Sprinkle some potato/corn starch and coat the shrimp. Potato/corn starch will absorb the smell and dirt from the shrimp. Rinse the shrimp under running water.
[Optional] To get rid of the smell, you can add 1-2 Tbsp sake and rub with your hands. Discard the liquid after 10 minutes (no need to rinse).