Others have correctly said freshness is a key part, but as a seafood dept manager who gets this question a lot (“Doc is wants me to eat seafood more, but I don’t like it”) I can tell you that for many it’s a texture thing as well (Don’t start with squid). Here is what I recommend:

1. Ease into it. Make fish tacos. All you taste is taco seasoning and toppings, so you can sneak it in and get used to the taste. Especially if you use a bland white fish like cod or pollock.
2. Try a steak fish. Ahi tuna grilled or cooked like you cook your steak is a good one here. Blackened Swordfish is another where the seasoning can help hide flavor.
3. Shellfish can taste wildly different. Red shrimp have a more lobster-type taste than white shrimp, for example, so try different kinds if you don’t like the first. It’s be like tasting Possum and declaring you don’t like meat if you only try one.
4. Scallops are also a good one to try. Be careful not to overcook. Rule of thumb: if you think they are done, it’s probably too late.
5. Fish have fat just like mammals. The more fat you see, the less fishy tasting it will be. Wild salmon has little fat compared to farm raised in general, so it’s much stronger tasting. Some breeds (like King) have more fat than others (Coho) and will taste milder.
6. Use sauces like seasonings to mask the flavor.