Turn off the ceiling fan.
Tighten the light bulbs so that they do not rattle. Loose light bulbs are often a source of humming on a ceiling fan. Turn on the fan and see if the humming has stopped.
Tighten the screws on the light globes with a screwdriver or by hand, depending on the connection. Stretch a silencer band, available at hardware stores, over each globe and place the band over the connection area.
Remove the pull chain from the unit if it is touching any of the globes.
Loosen the screws of the fan canopy if it is touching the ceiling and lower it slightly.
Tighten the fan blade brackets with a screwdriver.
Tighten the screws on the motor housing.