Moisture builds up quickly inside a flute, so cleaning it after each session is essential. Use a soft, lint-free cloth threaded through a cleaning rod to gently swab out each section, working from the headjoint down. Avoid touching the pads or using any liquid cleaners: a dry cloth is all you need.
Wipe down the outside of the instrument to remove fingerprints and oils, which can tarnish the finish over time.