I voted weekly, but there's a huge caveat to why. I used to clean it daily, and that was the cup and neck of the skimmer. Then one day I stumbled upon a video by Avast Marine showing their Skimmer Swabbie. It was love at first sight. I run it eight times a day for 2 minutes each. The neck of my skimmer is always clean, and I have the waste going to a waste collector. When the collector is full, it shuts off one of the two pumps going to my skimmer. The skimmer runs at half mast until I empty out the collector, still building a foam tower within the body of the skimmer in the meantime. I clean the cup weekly just because I like my gear clean.
The pumps are cleaned every six months, and the body once a year.