When buying fresh squid, choose small and whole seafood with an ocean-fresh fragrance. Allow 1/2 pound per person. It should be refrigerated, airtight, no more than a day.
Frozen squid can be purchased clean in a variety of forms: whole, tubes and tentacles, tubes only, and sliced tubes. Frozen squid thaws quickly under cold running water.
Squid meat consists mostly of fine muscle fibers and no fat, accounting for its leanness (and toughness). It's low in calories and rich in protein and phosphorus, but it also has the distinction of being the seafood with the most cholesterol.
Most often your fish market has cleaned its squid, but in case not, here's what to do: Make an incision lengthwise down the mantle (tubelike body), and remove the innards and transparent "pen" (cartilage) by gently scraping them out with a knife. Cut away the tentacles and pop out the small round bony piece called the "beak." Pull away and discard the fine, purplish skin from the mantle; then rinse. Discard everything but the mantle and tentacles.
Small squid are more tender than large ones. To tenderize larger ones, pound cleaned flesh with a mallet until it's limp and satiny.
Cookbook author Mark Bittman's "2 or 20 minute" rule is a good one: Cook squid quickly in a very hot pan for no more than 2 minutes; if it cooks any longer and toughens, continue cooking it at more moderate heat for about 20 minutes, by which time it should be tender again.