Avoid getting water in your ears while swimming / bathing.
Dry your ears after showering.
Occasionally a hair dryer can be used to blow dry the ear (care to be taken)
Avoid putting cotton in your ears.
Avoid scratching the skin outside and inside your ears eg. Ear buds, keys, tooth picks, finger nails etc. as this may cause skin abrasions and make it easier for a fungus to invade the eroded area.
Avoid putting objects in your ear
Use prescribed ear drops if water gets in your ears.