I think you already know what I am about to say. All seafood is delicate and is easily destroyed by overcooking, whether that is boiling, steaming, frying, grilling or baking. Overcooked seafood is dry and tough. Properly cooked seafood is tender and moist.
Beyond texture, overcooking seafood changes the taste from sweet and succulent to virtually tasteless ... a bit like the cooks who overcook the seafood. Well, if you are the one dining, your opinion of the cook will not be good.
Conversely, if the person cooking your seafood is knowledgeable and talented you are in for very nice pleasure, and the cook will have your liking and respect.
With that lead-in I have to be brief so as not to make this Primer long instead of short. I have listed just a few of the most important points below.
1. High heat (300 degrees F or higher) is perfectly fine when baking, frying or grilling seafood. It is the cooking time that toughens flesh, typically by drying it out, ergo losing essential moisture from the flesh instead of locking it in.
2. Don't cook seafood in a dry environment. Use oils or butter, batters, water, steam ... whatever will help maintain the moisture in the seafood, yet help cook it. The easiest examples are batters used when frying that lock in moisture, or butter on the surface of fish when baking.
3. Minimize the cooking time. Seafood is so delicate that any effort you make to "be sure" that it is cooked is most likely to destroy it. Properly cooked seafood is barely beyond raw. If that bothers you then simply consider sushi and sashimi ... when prepared from fresh seafood they are perfectly healthy to eat.
4. You typically don't want translucent flesh, as that means the seafood is still raw, unless, of course, you are having sushi or sashimi. That means you should check the interior of what you are cooking until you gain enough experience to time your cooking with confidence ... based on the type of cooking and on the thickness of what is being cooked and on the heat level and type of heat being used.
5. A simple example is the cooking of a fish chowder, where the entire chowder is cooked before adding the raw pieces of fish, after which the chowder temperature is maintained barely at a simmer to allow gentle cooking and a short cooking period, to keep the fish tender.
Okay ... that's it. When you see directions for cooking any individual seafood dish in Food Nirvana, follow those directions carefully. Use a timer. Use an instant read thermometer. Do these things until you become an expert and can sense what to do automatically.