Make sure that the pond has partial shade for the fish. This provides relief to the fish in warm periods of the day. This shade could come from any nearby tree or artificial construction beside the pond.
The pond needs to be kept clean for the fish to live in a healthy medium. Scoop out any physical impurities including leaves that you see inside the pond on a daily basis. Do not let them rot inside the water. Installing a filtration system and UV clear can help in keeping the pond clean.
Regarding pond plants, keep them trimmed. Prevent their dead materials from falling into the water. If there are many lilypads covering the water surface, the fish underneath will not have much oxygen to breath.
During summers, the metabolism rate of the fish is high. Keep feeding the fish rich fish food during these months. When winter approaches, the metabolism rate decreases. The feeding rate should be decreased to once a week as the fish get dormant. The feeding needs to be stopped completely when the fish stop coming to the surface. They will stay at the bottom during the hibernation. You will know when to resume when the fish start appearing again on the surface.
During winters, most pond surfaces can freeze due to the cold. This can create breathing problems for the fish below as they do not get oxygen to breathe. The layer of ice needs to be broken to let in air for the fish. However, any sharp or heavy instruments cannot be used for this as they cause tremors through the water. An aquarium heater can be used instead.