Provide your kitty with plenty of things to do and stuff to scratch, such as cardboard, wood, or rope.
Make scratching posts more appealing to your cat by spraying them with a bit of catnip (you'll want to do this outdoors or over hard surface to avoid getting the catnip on the carpet).
Cover any carpeted areas that have been scratched by your cat with flat, heavy objects (ceramic tiles or rubber mats work well) for a few weeks with the hope that breaking the habit of tearing up a particular area will make your pet "forget" about it.
Lightly spray your cat's favorite area to scratch with a spray bottle of water mixed with a few drops of citrus oil. Cats hate the smell of citrus so this could be a good deterrent.
Block access to rooms that you think your kitty cat may cause problems in, especially when you're gone. Just be sure to give your cat plenty of things to do while you're away to keep him/her out of trouble.
