This depends entirely on how much stuff goes through your drain but ideally, you want to spend more time inspecting your drain during autumn/fall. This is the period when the leaves start to fall and most of them will head towards your drain. Take at least ten minutes of your day to scoop the leaves out of your drain then properly dispose of them. If you don't do this regularly, you will eventually have a build-up which will lead to you using more effort and time of your day to fix.