Summarize:

If you are working with frozen fish, you might want to take it out of the freezer and let it thaw in the fridge. Do not let it thaw in the kitchen, or it may spoil. Gently massage the flesh to get rid of any watery residue or scales. Pat the fish dry, then season it with olive oil, herbs, or a marinade. Unlike beef, chicken, and other types of meat, fish soak up flavors quickly. Most fish only need to be marinated for 15 to 30 minutes; tuna can be marinated for up to 4 hours. Rinse your fish fillets or steaks, and pat them dry with paper towels. Soak them in your desired marinade and leave them in the fridge so that it does not spoil. Once they are done marinating, grill them. If you are not marinating the fish, consider brushing on some olive oil along with your desired seasoning instead. This helps the flavors penetrate into the meat better. Chill your fish in the fridge or freezer until it is stiff. Cut the fish into ½ to 1 inch (1.27 to 2.54 centimeters) thick slices using a sawing motion. Trim away any belly fat or bones. If needed, peel away the skin. If you are making salmon, consider leaving the skin on. The skin will help hold it together while it grills. It comes off easily once the fish is cooked. Cut the fillet width-wise into four smaller pieces. This will make the fish easier to handle in the frying pan. For seasoning, try coating the fish with a mixture made from a beaten egg and water. Dip the fish into cornmeal or breadcrumbs seasoned with salt and pepper just before you toss it onto the frying pan. This is great for delicate fish, such as sole. Brush some oil or melted butter onto the fish; this will keep it moist. Next, add some dried herbs, such as basil, rosemary, dill, or thyme. You can also use spice blends, salt, pepper, or even minced garlic. A squirt of lemon is great for any type of fish. If you plan on serving salmon with a sauce, stick with a simple sprinkling or salt and pepper. If you don't plan on serving the salmon with a sauce (or are keeping the sauce optional) try the following seasonings:  Sprinkle on some herbs, such as basil, dill, or thyme. These work great if you want to grill the salmon. Remember to brush on some olive oil before grilling it. Add some minced garlic. Try a seasoning blend. Look for something lemon, pepper, or herb-based, such as: garlic pepper, lemon pepper, or Italian. Brush some olive oil and lemon dress onto tuna and season it with salt and black pepper. For more flavor, sprinkle on some fresh herbs, such as rosemary or tarragon. Tuna works great with Asian marinates, such as teriyaki sauce. Marinate it for 15 minutes to 4 hours in the fridge before grilling it.
Allow frozen fish to thaw in the fridge before you cook it. Rinse the fish before you season it. Work quickly if you plan on grilling the fish. Consider cutting shallow slits into the side of skin-on fish before seasoning and cooking it. Consider cutting large fish, such as salmon or tuna, into steaks for grilling. Consider cutting fish fillets into smaller pieces before pan frying them. Season fish fillets with oil, herbs, and spices before baking them. Season salmon lightly or heavily, depending on how you will serve it. Season tuna with olive oil, lemon juice, and herbs before baking it.