I have a cover on mine so no light gets in there to grow algae. Once every six months i pull the pipe grate off and clean it. Periodically I use my iPhone to look in from behind to make sure there aren't any critters trapped in there. Beyond that, nothing.
I'd definitely recommend getting/making an opaque cover for your overflow. It keeps the light out, which will prevent algae from growing. I keep meaning to do something better, but for now my cover is a 5-gallon bucket lid cut down to 1/3 its size.