Each week you should do the following.
Wipe the inside of the glass down with a clean fish sponge.
Do a 50-75% water change and gravel clean the substrate every week. However, if you get an ammonia or nitrite reading above 0ppm, or a nitrate reading above 20ppm then do a 75% water change every day until its 0ppm.
Use a basic model gravel cleaner like the one in the following link to drain and gravel clean the substrate.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.
Aquarium cleaning should take 30 minutes every two weeks. Learn how the professionals do it in 18 easy steps.
www.about-goldfish.com
-----------------
You should clean the filter at least once a month. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.