Read the label of cat foods to pick the best food for your cat.
A few things to look for are:
Meat as a first ingredient and not meat by products or grains.
No food coloring - this can cause intestinal and skin allergies. Food should look natural or brown. It should not be red, green, yellow or any other bright color.
No chemical preservatives - if you cannot pronounce the names or it doesn't specifically say that the ingredient is a source of a vitamin or mineral then you don't want that food.
PH balanced for urinary health - be careful with this one. Most foods for cats are designed to create an acidic urine to prevent the most common urinary crystal. If your cat doesn't have a urinary problem already then try to find one that is designed to create a neutral pH rather than an acidic one.
Feed cats a combination of can and dry if possible, with can food being at least ¾ of the daily ration and dry food only a small snack. Cats can often become fixated on textures of foods and, if they are not used to different textures, will not recognize them as food. This means that a cat that is not used to can food may refuse to eat entirely if not given dry food. Unfortunately can food is often the primary food offered to sick cats in the clinic environment or in an attempt to coax them to eat since can food has more odor and taste to it. Introducing a sick cat to a different texture food is not usually a good idea.
Quantity - Most cats need to eat about 1/2 to 3/4 of a 5 ½ oz can a day divided into at least 2 meals. Top this with no more than 1 tablespoon of dry food per meal. Those cats that refuse can food need about 1/2 cup of dry food also divided into multiple meals. Indoor cats especially will eat more if it is available from boredom, to take it away from the other cats or from sheer gluttony and will gain weight. The total volume an individual cat needs to eat will vary based on its age and activity level which is one of the things that is monitored with regular physical exams.