If the oyster is open and doesn't close when tapped on the shell, do not buy it. To test closed oysters, knock two of them against each other -- if they sound hollow, don't buy them, as they've already died. Fresh oysters should feel heavy and full with water, and dead oysters will be light and empty.  Fresh oysters should smell like a sea breeze. If they are fishy or odd smelling, don't buy them. If you need to store oysters, cover with a damp cloth in the fridge. Do not cover or seal with plastic wrap -- oysters are living creatures and cannot be suffocated! a thick, dull-pointed blade for shucking. While you can use any knife, chances are good you'll break them beyond repair if you aren't careful. A dedicated oyster knife is, by far, the most efficient way to proceed. Be sure to really get in there, scrubbing away any excess dirt and sand. When done, leave them in cold water as you shuck, keeping them cool as you work. Note that, while this cold water will drown the oysters, you are about to cook them. As long as you are shucking right before cooking, it will be fine. This allows you to drop the oysters, along with their desired liquids, into a cooled area while you work. Shucking takes some time, and you do not want your shucked oysters to go bad while you're at work on the other ones. Look lengthwise across the shell. You should see where the two halves meet, with one shell is relatively flat and the other has a rounded belly. The rounded half is the bottom of your oyster. It can be hard to find on some oysters, but some practice will make it apparent. The hinge is where the two shells meet. Position the towel so that the hinge faces your dominant (cutting) hand. You want the oyster in the towel like a hotdog in a bun. This towel will protect the hand holding the oyster down and keep things from sliding as you cut. You are not trying to drive the point into the oyster. You're just trying to get a "foothold" in the hinge, which will allow you to use the knife to pry the shell apart. It can take some time to find this sweet spot, but all oysters have them. " Again, this isn't brute force -- you're not jamming the knife into the shell so much as using it to create space between the two shells. Keep working the knife up, down, and around until you feel the oyster yield and pop. Once you've got the oyster started, push the knife slightly further in and twist 45-degrees until the wide part of the blade prying the shells open. When done, whip your knife off on the towel to remove any extra mud or dirt stuck in the hinge. Keep the belly of the oyster flat on the towel to ensure none of the liquid drips out. This cut severs the muscle keeping the oyster closed. Simply cut across, using the top shell as your guide. The oyster, tucked safely in the belly, will await with its liquids as long as you keep it steady. If, upon opening, you smell a fishy smell from the oysters, toss them out. Use your knife to pry the oyster out of the bottom shell, juices and all. Check to make sure no bits of shell flaked off into the oyster meat, then simply dump everyone into your bowl and keep shucking. If you find a tiny little crab in the oyster, just toss it out -- these little oyster crabs won't affect the final flavor or freshness of the oyster.

Summary:
Only buy fresh oysters if they are closed tight, or close immediately when touched. Purchase an oyster knife: Rinse and scrub all the closed oysters under cold water. Set up an ice bath by filling a large bowl with ice and water and nesting a smaller bowl inside of it. Find the bottom of the oyster and place it on a small towel. Using half of the towel, cover up all of the oyster but the hinge. Poke the tip of your knife into the hinge, searching for a place you can easily pry the shell apart. Twist and pry the knife to lift the shells apart, prying until they "pop. Turn the knife perpendicular to the oyster to pop it open even more. Cut along the flat top shell to completely open the oyster up. Dump the liquid and oyster in your cool bowl, toss the shell out, and repeat.