Welcome to fluther. I would say vacuum the carpets every month or so, depending on your traffic and how dusty they get. Upholstery about every three or four months. But I’m a guy so I may be a little lax.

Part of the decision making is determined by whether you have kids and/or pets.

When you say clean, do you mean vacuum or do you mean steam clean?

BTW, welcome to Fluther.

Vacuum the cushions one a month, the carpets once a week. Do other cleanings when required by the presence of dirt and crud.

I’m assuming the OP does not mean vacuuming, but deep cleaning. I need to vacuum daily due to pets and children.

Low traffic areas can be cleaned every 12 to 18 months. It’s suggested that you should clean high traffic areas 2 to 4 times a year.

Never, I don’t have any carpet or rugs. That’s the way to go…no sinus trouble anymore. I do clean the couches every now and then.

Vacuuming: I would say at least weekly if you have kids, pets, or high traffic, less if you don’t. Same goes with upholstery.
Steam cleaning: Probably when the seasons change, get the steam cleaner out. If it’s been a couple of months since last cleaning, definitely steam clean carpets. Upholstery, it depends.