Keep your pond aerated and filtered 24 hours a day. Keep your pond clean of debris on the bottom. Watch carefully for anchor worms, lice and other parasites. Medicate with Dylox every 3 months to kill and control parasites. Use a chloramine remover whenever adding fresh tap water.
Most cities have chloramine in their tap water.
Have medication and chloramine remover on hand for emergencies. Have a spare tank or aquarium for use as a hospital to treat sick or injured koi. Remember to aerate and filter 'hospital tanks'. Periodically clean the filter. Most filters should be cleaned at least twice a year even though the water looks clear.