The first area is correct diet which is covered in another article on this website. A good healthy natural organic diet will go a long way to making your pet much more healthy without even making a trip to the veterinarian. Exercise is also important. Cats benefit from a scratching post and can be played with to encourage them to exercise. I do not recommend declawing as this is extremely painful, and can have long-lasting traumatic effects.
Cats are such beautiful animals and left in their natural state are much healthier and happier.
If a cat cannot go outdoors then try and provide some way they can play and toys they can enjoy. Another cat as a companion often works wonders to spice up the life and activity of a couch potato cat. Try to decrease the use of all chemicals in on and around your pet. Both you and the animal will benefit. There are effective organic and natural alternatives to harsh chemicals in most cases.