A little training when your cat first comes home will help to prevent any bad habits from becoming established. If you try to "think like a cat" to discover why they perform a certain unwanted behavior, you can help to establish more acceptable routines. Here are some tips on the three most common bad habits:
Scratching is a normal cat behavior to leave its scent on its territory, get exercise, and groom its nails. Most cats will leave your expensive furniture alone if you redirect their scratching instincts to an acceptable spot. Invest in a kitty condo big enough for your cat to stretch out on, and if you see him scratching, take him to the post. Rub a little catnip on the condo to enhance its appeal. You can also put strips of aluminum foil down the edges of your sofa during the training period as a deterrent. And have a spray water bottle handy to spray your cat while firmly saying "NO" if he scratches the couch.
Cats love high places, so the kitchen counter strikes them as a great place to watch the world go by. If your cat also finds food up there, they've just had major reinforcement for this bad habit. Best solution: find another spot in the kitchen where its ok for your cat to hang out from on high, like the top of the refrigerator. Then persistently move your kitty there every time she jumps on the counter. Repetition and consistency are key here, but eventually your cat will get the idea.
3. Not Using The Litterbox.
First, have your cat checked by your vet to rule out a urinary tract infection. Next, try changing the type of litter, for many cats are very sensitive to particular litters. Try unscented litters, removing hoods from boxes, moving the box to a more private location, or cleaning the box more often. Provide multiple boxes in multiple cat households. Also, if you have a kitten, be sure it actually remembers where the litter box is! Sometimes in a big house a small kitten can get lost, in which case it will look for the nearest unobtrusive corner to go!