Many cat owners suffer with cats scratching in unwanted areas such as furniture. One of the reasons behind the scratching is that cats are very responsive to different smells in the area. So, the solution is easy - change the smell to something the cat will dislike. Most cats do not like the smell of citrus or bitter apple sprays so you can put in these in areas to deter your cat from scratching. Another non-harmful technique is to use a water bottle to spritz the cat anytime he or she is scratching in an area you dislike. Most cats won't like this and it will remind them to not keep participating in the same behavior that is causing them to get sprayed with the water.
You will need to provide the cat with an alternate scratching object such as a scratching post. Positive reinforcement will encourage the cat to use the scratching post, rather than your big, comfy sofa. Training a cat is similar to training a dog in the sense that cats also respond to negative and positive reinforcement. Anytime your cat is scratching on something you don't want her to, make sure you tell her 'no' and put her next to the scratching post. Catnip can also be used to aid in encouraging the cat to use the scratching post instead of furniture.
