Salt and Protein. Without fully understanding your question, in general, kidneys are healthiest and happiest if they are given a little extra water, and, no excess salt or protein. Excess salt and protien are just extra work for kidneys.
Kidney care. Exercise regularly, eat sensibly with lots of fruits and vegetables, less meat, more beans and legumes, don't smoke, and don't eat alot of salty food or use a salt shaker. That's right, your kidneys are in large part an extension of your cardiovascular system, so caring for them is just like caring for your heart.
Water. Without knowing more specifics about your request; the best way to insure proper renal (kidney) function is to maintain adequate hydration; drink plenty of water!
Drink plenty of. Water, keep blood pressure under control.
Kidneys. It is very important to keep your blood pressure under control. If you have diabetes, blood sugar control is also imperative. Keeping your cholesterol controlled also can help prevent hardening of the arteries going to the kidneys. Keeping well hydrated is important. Avoiding or limiting the use of nsaids (ibuprofen, advil, naprosyn) can also help.
Easy. If you are an individual without a history of kidney disease, or a family history, then its the typical things: eat right, exercise and hydrate yourself. Avoid harmful things such as unsafe supplements, drugs, smoking. See your physician regularly. If you do have kidney disease then there are other things we do for prevention.