Start with observing the ear; this prepares you for the vet visit. (To be really certain what is going on, you do need the vet.)
- Coffee ground colored granules that dissolve into reddish-brown are classic for ear mites.
- What does it smell like? A really foul smell may be yeast or bacteria, and will require a vet visit for treatment.
- Is there any observable bright red bleeding? Scratching or ear drum rupture may cause bleeding.
- Can the cat hear out of the ear (if not known to be deaf)? - fingers rubbing together, clicking, etc may cause at least an ear flick acknowledging the sound.
- Does the ear seem painful? Infection/abcess/severe mites can do this.
For simple cleaning in the cat that has excessively waxy ears, there are veterinary ear cleaners at many pet stores. Use a cotton ball dipped in the cleanser. Place the entire ball into the ear and massage from the outside (this gets the solution deeper in the canal). Remove the wet cotton ball and quickly wipe with a dry one ... or you'll get showered with the cleanser and any debris that has loosened enough to fly out (been there, done that!). Repeat if its really gunky. Do both ears ... or at least as much as the cat will tolerate ;-)