The key to getting fish right is knowing what to buy. That's why we're so grateful for Mark Bittman, who streamlines the process by dividing all fish into three basic groups: thick fillets, thin fillets, and steaks. Learn your types and you can do any recipe with whatever fish is freshest at your market—no more hunting down a certain species just to make dinner.
So start with what looks good and use it in one of these incredibly great recipes.
Some of the fish on this list—most notably the so-called flatfish, such as flounder and sole—are about 1/4-inch-thick and cook in as little as 2 minutes; others are a bit thicker.
You can always substitute the sturdier fillets in recipes that call for a thin cut (just cook them a little longer). But if you try to treat these delicate fish like the sturdy thick ones, they will break apart during cooking.
This is what you get when the fish is cut all the way through into a piece that's essentially a cross section. With really large fish (like tuna and swordfish), a steak is boneless. With smaller species (like salmon) there are bones and skin.
Steaks are sturdy, which means they'll hold up on the grill; since they're of uniform thickness, they usually cook evenly, at 8-10 minutes per inch of thickness.