It depends on how big your tank is, what sort of filtration news got, and how many fish in the tank. Your substrate will also pay a very big part in the cleanliness of your tank.
If your tank is quite small, you'll probably find that tank maintenance is absolutely necessary once a week, that will include cleaning the gravel, and quite a substantial water change.
The bigger the tank, the less the maintenance is required. Obviously if you don't ever stop, that's a big help as well. Nitrate levels won't rise so quickly so water changes don't have to be so big. Adding really good filtration to your tank will mean that they remove a lot of the waste.
A weekly water change is recommended. There are exceptions though, if you have a very large tank and you don't overstock it, you can go for more than a week without having to change the water. The best thing to do is monitor your water conditions. This will give you an idea of how big a water changes is needed.
This is why we recommend using large tanks and good filtration, they'll save you a lot of hassle in the long run.