Every month
Call the phone number published on the homepage. Send the contact form to an inbox a person reads. Open the busiest service page on a phone and tap the call button.
Remove offers, staff, and hours that are no longer true. Outdated promises create bad leads and contradict your listings.
Every quarter
Check the domain expiration and the hosting bill. The business should be the owner on the account, even if a developer has access.
Click through the top navigation. Broken links and images usually show up on pages nobody edits. Look at Search Console, if it is verified, for pages that suddenly stopped being indexed.
After any redesign or plugin update
Recheck titles, the contact path, and redirects from old URLs you still print on cards or ads. A redesign that orphans the old service URLs throws away whatever those URLs had earned.
If the update made the site slow or uneditable, that is a maintenance or technical SEO job, not a reason to ignore it until the next marketing push.