I need to clean Abbey's at least once a week--they're long, and if she is out a lot, the moisture gets trapped in there and could lead to infection--she had an ear infection when we first got her, and it was not fun giving her the drops to help it heal.
I have ear cleaner I got at the pet store, and I use a cotton ball. They also make ear wipes, which you can just use to clean the ear, no worry about peroxide, water, or alcohol--the pad is already damp.