Ways to Correct Furniture Scratching

Kittens
If a kitten starts to scratch your furniture gently pull it off and place its front paws on the scratching post or appropriate cardboard or sisal mat. Do not yell at the kitten and do not ever throw anything at the kitten. This will result in the kitten being scared of you and will do nothing to correct the behavior.
Also, use horizontal scratching surfaces that lay flat.

Older cats
Gently shake an empty soda container containing 3 or 4 pennies, but not directly in his or her face. Put double-edged-sided tape or aluminum foil on the furniture. This will reduce the scratching sensation. Also, you can purchase little cat “booties” (Soft Paws) to slip over the cat's nails.
And, as with kittens, use horizontal scratching surfaces