Housing:

Cornsnakes do best when housed individually (cannibalism can and does happen!).  The cage should be big enough for the snake to stretch out in comfortably.  A good rule of thumb is that length + width should be atleast as much as your snake is long.  Height isn't particularly important, but since corns are semi-arboreal, they will climb if given room to do so.  For most corns, a 20 Gallon Long (not High) aquarium is adequate for an adult.  Keep in mind that snakes are excellent escape artists, and if your cage isn't secure, they WILL get out.  (If  you're lucky enough to find your escaped snake, make sure you fix their escape route as they WILL get out the same way again, and much faster the second time.)  NEVER use tape in an enclosure.

Some form of heating is a requirement, as cornsnakes are reptiles and can only regulate their body temperature by travelling to warmer or colder areas.  I recommend some type of under-tank heating.  The warm side of the cage should be in the mid-80's Farenheit, and the cool side in the mid-70's.  A waterdish that the snake can climb in and out of easily should be placed in the center of the cage.  Hides just barely big enough for the snake to squeeze under should be placed in various places around the cage; atleast one on the cool side and one on the warm side.  Cornsnakes, like all snakes, will spend most of their time hiding.  Substrates to use are: Aspen shavings, papertowels, and newspaper.  Substrates to avoid are: Pine (dusty), cedar (toxic!), and sand.

A word on cage placement: pick some place that's not in direct sunlight, and avoid drafty locations.  If you have cats, dogs, or ferrets, pick a location that they cannot access (a room with a closed door), as they may try to 'play with' or to eat your snake (especially cats and ferrets).  Larger mammals also have a habit of knocking cages over, allowing snakes to escape.

Feeding:

Corns should be fed frozen-thawed mice of the appropriate size (up to 1.5 times their widest width) roughly once a week.  Hatchlings should be fed every 5-7 days, adults every 7-10 days.  Corns can also be switched over to rats of the appropriate size, though there are no rats small enough for a corn on mouse pinks to eat.  Adult corns which are big enough can also be fed chicks.  A good rule of thumb is to wait two days after feeding before handling your cornsnakes, to give them time to digest.

Behavior:

Most cornsnakes do not bite, but some hatchlings and even a few adults may do so if they feel threatened.  The worst they can do is break the skin (yes, they do have teeth) and cause a little bleeding.  If one bites you, you should hold still until it lets go.  If you jerk, you can pull out some of their teeth.  Wash the area with soap and water, especially if it's bleeding, and you'll be fine.  (By the next day, the wound will hardly even be visible.)  Cornsnakes will also vibrate their tail to warn you that they don't wish to be disturbed.  Most corns will spend their time hiding, but after a month or two, you may see them out and about, especially around feeding time.

Handling:

Cornsnakes in a new home should be given a few weeks to adjust, before you start staring at them and handling them.  Handling should be for short durations (15 minutes) at first, but as the snake calms down, you can begin having it out for longer and longer periods (though it may choose to go to the bathroom on you).  Do not pet the snake on the head, as most are sensitive about being touched there.  Instead, just let the snake crawl on your hands, arms, and shoulders.  Never hold the snake as if it were a stick.  It's a living animal and its weight needs to be properly supported.  As with any animal, wash your hands after handling it.

I've only touched on a few areas here... there's lots more information within The Cornsnake Manual.  If you're interested in the different color and pattern morphs, I recommend Cornsnake Morph Guide, which is updated yearly.  Be sure to find a knowledgable reptile vet to bring your snake to if it gets sick, as most vets do not know much about reptiles.  Have fun and goodluck!