Ongoing work.
MONTHLY
Check Search Console for new errors Check indexed page count Check for not-found errors worth redirecting Review any pages losing position
QUARTERLY
Check site speed Check mobile usability Review redirects for chains Check the sitemap is accurate Check structured data is valid
ANNUALLY
Review site structure Audit thin pages Review internal linking Check every listing and profile matches
AFTER ANY CHANGE
Check the visibility setting Check robots.txt Check key pages still resolve Check redirects are in place
AFTER A REDESIGN OR MIGRATION
All of the above, immediately.
WHAT TO RECORD
What you changed and when.
That record is how you explain a traffic change months later.
WHAT NOT TO DO
Check once a year and wonder why traffic fell.