A cat's scratching instinct has to do with their need to stretch their claws. It is a natural craving to stretch, just like it is for us humans. It’s an instinctual need for a cat, so you cannot stop your cat from scratching. What you have to do is provide them with the appropriate place to do so.
Try using a sturdy sisal, fabric, or rope-covered post that’s tall enough for your cat to reach and stretch on (at least three feet tall). If you have room, you can invest in a piece of kitty furniture that has a built in scratching post. Another less expensive option is to use a cardboard scratch box or bar of sisal. Often if the scratch post is rubbed with some catnip, the cat will become attracted to it and more interested in using it instead of your furniture. Sisal has an added benefit in that it will actually file down your cat’s claws.
Placement of the post is very important. Put it in a room that your cat enjoys spending a lot of time. Try to place the post near or right in front of the furniture he tends to scratch and bring him to the post whenever he tries to scratch the furniture or rugs. Initially, it can be effective to have the scratch post in the middle of the room so that the cat is reminded of it often. As they grow fond of the post, it can then be moved to a less conspicuous location.
Another deterrent from scratching your furniture or drapes is to add double sided tape or tin foil to the areas that they chronically scratch. These surfaces are not pleasant to scratch and after some time, the cat will abandon these areas for scratching. Once you see that kitty has started to use the scratch post instead, the tape or foil can be removed.
Stubborn cats often get the hint when a firm, loud "NO" is used or a loud clap or noise-maker when you catch them in the act of scratching on an unsanctioned item. The key is to make the noise at the very moment that they do scratching. Any tactic you use to train your cat will not work after the fact.
It is often more effective to show your cat what to do rather than scolding them for things not to do. This is a better tactic than reprimanding your cat. Lavishing lots of praise and affection on the cat when they use the scratching post is a great positive reinforcement that encourages post use.