SOME QUICK AND SIMPLE IDEAS:

STRONG TASTING FISH:
    Salmon, Tuna, and other flavorful fish can be soaked in cold water for about 30 minutes. This will help remove salinity and will help clean the fish beyond original processing and handling.
    Sprinkle or marinade with lemon juice or a vinegarette dressing, AND/OR spice it up with a little pepper and garlic. You can optionationally use cayenne pepper to add heat.

MILD TASTING FISH:
   Some shark, cod, bass, and many freshwater or other "milder tasting fish" can be lightly seasoned or marinaded. Keep in mind that over seasoning may take away the flavor of the fish.

OUTDOOR COOKING:
    An interesting method of barbequeing is plank cooking. Soak a thin wood plank (1/2 in. or less thick) in submerged water for a couple of hours. Put the wood plank on the grill and slow cook your fish on the plank. Of course, you can choose from a variety of clean and untreated woods for different flavoring. ********DONT USE PLYWOOD OR TREATED WOOD *******

Of course, follow all USDA and other safe handling instructions on retail products. These instructions are also a good guide for any market fish.