From EHow.com

• Cats can be happy indoors if they have a companion pet, toys, scratching posts, window shelves and lots of attention from you.
• You might be able to train your cat to walk on a leash or harness - but watch out for dogs.
• Hold your cat with one hand under his chest and the other hand under his back legs, keeping it close to you.
• Play with your cat or kitten with toys, not your hands, which can encourage biting and aggressiveness. If your cat bites, blow in her face before pulling your hand away.
• Reward your cat when she does good instead of using physical punishment when she's bad. Physical punishment will only make her afraid of you or cause her to act out when you're away. A loud noise or squirt of water can help stop bad behavior.
• The outdoors poses many possible dangers including fights, disease, getting lost, traffic, hypothermia, traps or the possibility of being stolen.
• Small objects such as buttons, needles, shoelaces and tinsel can be hazardous if your cat eats them.
• Keep household cleaning chemicals and medication in places safe from your cat's curiosity.
• Certain plants, such as poinsettias, can be fatal for your cat, as can the water at the bottom of your Christmas tree.
• Take uneaten food away from a kitten after ten minutes - overeating can cause diarrhea or vomiting.
• Your cat can be strangled or suffocated by plastic bags with handles.
• Give your cat its own "garden" (from a pet store or vet) so it won't eat your plants, which can be poisonous. Or, to prevent plant eating, place cedar blocks or hot chili peppers on the soil, or hang the plants out of your cat's reach.
• Hide electrical wires.
• Keep toilet lids down.
• Make sure your window screens are secure - cats don't always land on their feet, and they don't have much depth perception.
• If your cat refuses to use a clean litter box see your vet - it could mean a health problem.