Back in the days, performing water change once a month approximately 15% was regarded as normal. It was considered IDEAL if you could do it every 2 weeks. Nowadays, many of us are doing it weekly, which is fantastic.
As mentioned above, the frequency and volume of water change really depends on your system - i.e., fish stocking levels, feeding regimen, water quality (RO/DI, tap) etc. I would start out with a general 20% every two weeks to see how your tank appears. Main thing is to keep a level of consistency. Our corals/fish really benefit from stable environments. Good luck!