The frequency of cleanings on an aquarium really depends largely on the stocking density of the tank. Every tank is unique. Every tank's a little bit different. So it's hard to set a general rule that applies to all environments, all aquariums. But as a general rule of thumb, I like doing a good water change every two to three weeks. If the tank is not stocked that heavily and you're an advanced aquarist, you know what you're doing, you can get by with every four to five weeks to flush out some of the waste and introduce new minerals and trace elements into the water, which is one of the main reasons why you're doing a water change. But typically, every three to four weeks, you want to do a good overhaul on the tank.
If you're fortune enough to have the time to do it every week, I recommend doing a small filter cleaning every week and then doing a small water change every other week. That's probably the best method. You're going to shock the system the least. You're cleaning filtration on a different week than you're doing the water change. So again, you're reducing the stress in the aquarium. The more you do to an aquarium, the more stress you put on it, the more stressed the bacteria is, and the higher the chance of having maybe a bacterial bloom, or an ammonia or nitrite spike, after you do your maintenance. So you want to break up the intervals of how you clean the aquarium. But typically, every two to three weeks is when you do your typical maintenance. You clean your filter, you do your water change, and then every week, you can clean the viewing panel if it starts to get some algae or bacterial slime built up on it.