For a lighter fried dish, after you cut up the calamari, dip in milk and then in flour. Shake off excess flour (use a sieve so that the flour falls back in the bowl) and deep fry just until the flour is golden, less than a minute. Drain, salt, and yum.
(This is how I did it when I was "calamari girl" making the amuse at Le Bernardin.)
Good advice about sautéeing quickly. I like to marinate whole small calamari in oil and spices first, then drain and toss in a very hot cast-iron skillet. Again, just a minute or so is all it takes.
You can also make a bread crumb-cheese-herb mixture, stuff it into the bodies, and then braise them in tomato sauce for 45 minutes or so. Throw in some fresh green peas near the end, and serve with rice or pasta.
The general rule is cook it for 45 seconds or 45 minutes; nothing in between. It gets tough in the middle range and then needs the long cooking to soften again. (I'm supposing that the time for the frozen rings is just to thaw and cook the coating.)