This script should run at least weekly, and preferably daily. Remember that certs don’t get renewed unless they are near to expiration, and monthly would cause your existing certs to occasionally be expired already before they get renewed.
The name of the program is certbot, which was renamed from letsencrypt. If you are still using letsencrypt, you need to update to the current version.
Aside from those issues, it’s about the same as my cron jobs.