If you’re lucky enough to have access to fresh soft shell blue crabs, you should also know how to clean them. It’s a very simple process- all you need is a pair of shears. You could use a knife, but it's a lot easier and faster with snips.
Though technically all of a soft shell is edible, some parts are less texturally desirable. Removing these parts before cooking is generally a good idea.
Step one: cut the face off the crab.
Step two: Fold one of the furthest points on the shell towards the center, exposing the gills.
Step three: Cut the gills out at the base. Repeat on the other side.
Step four: remove the abdominal flap.
Done.
Other things to know:
Don’t prep soft shells too far in advance, there will be a large amount of moisture loss. Clean them right before you intend to cook them.
Soft shells can be kept alive for a few days under the right conditions. Don't keep them on ice, it’ll kill them. Rather, put them in a cardboard or styrofoam box and cover with some damp newspaper. Store in the warmest part of your fridge or a cooler with some ice packs to the side. That being said, they are best extremely fresh, so plan accordingly.
If you find yourself in a spot where you have fresh soft shells, but no chance of cooking them before they die, you can prep them, wrap in plastic wrap and freeze. Frozen soft shells will lose a lot of moisture, so they won’t be as good as fresh ones, but some softshells are better than no soft shells.