How often
A healthy, upright ear with little hair often needs nothing more than a look once a week. Floppy ears, hairy ear canals, dogs that swim, and breeds prone to wax need cleaning more often, roughly every one to two weeks. Cleaning a healthy ear more than that removes the wax that protects it and can cause the irritation you were trying to prevent.
What a healthy ear looks like
Pale pink skin, a little wax, no smell to speak of. A dark, sticky discharge, a yeasty or sour smell, redness, swelling, pain when touched, or a dog that shakes its head and scratches at the ear are not cleaning problems. They are reasons for a vet visit, and cleaning first can make the examination harder.
Doing it calmly
Choose a moment when the dog is relaxed. Hold the ear flap up, fill the canal with cleanser until you see it pool, then massage the base of the ear for ten seconds; you will hear it squelch. Step back and let the dog shake. That shake does most of the work, bringing loosened wax up where a cloth can reach it. Wipe only what you can see with a soft cloth or cotton pad. Never push anything into the canal, and never use cotton buds.
What to use
An ear cleanser made for dogs, without alcohol. Alcohol stings an ear that is even slightly irritated, and a dog that has been stung once will not let you near the ear again. Water alone is not enough and leaves the canal damp, which is exactly what you do not want.
After swimming or a bath
Dry the ears. A gentle cleanser with a drying action after water helps floppy-eared dogs in particular, because a damp canal under a heavy ear flap is where problems begin.
When to stop
Any sign of pain, blood, a foul smell or a dog that repeatedly resists. Ears are sensitive, and infections are common enough that persistence at home rarely pays. A vet can see the eardrum; you cannot.