Spring
As the water warms, everything wakes up at once: fish, plants and the bacteria in the filter. Clear out leaves and debris that have built up over winter, check the pump and filter are running properly, and start feeding again gradually as the temperature rises. This is also when most planting gets done.
Summer
Warm water holds less oxygen, and a pond in full sun can get uncomfortably warm. Keep an eye on fish behaviour, particularly early in the morning. Top up evaporation losses with treated water. Blanketweed and algae are at their most enthusiastic now.
Autumn
Net the pond or clear leaves regularly, because leaves left to rot in the water cause problems through the winter. Cut back dying plant growth. As the temperature drops, move to a food suited to cooler water and then stop feeding altogether once it is cold enough.
Winter
Mostly, leave it alone. Keep part of the surface clear of ice so gases can escape, but never break ice with a blow, which can harm the fish. Check pumps and equipment are in a state you are happy to leave them in.
Thermometers are worth it
Much of the above depends on water temperature rather than the month. A cheap pond thermometer takes the guesswork out of it.
Ask us about pond foods and treatments for the season you are in. What suits in July is not what the pond needs in November.