Start with the accounts
Enable multi-factor authentication for every user, especially administrators. Avoid shared accounts, remove users who have left the company and make sure each admin account belongs to a real person with a strong sign-in method.
Protect administrator access
Administrator accounts should be limited to people who genuinely need them. Daily email and file work should happen from normal user accounts, while admin accounts should be used only for administration.
Review email and domain security
Check that SPF, DKIM and DMARC are configured for the company domain. These records help receiving mail systems understand which services are allowed to send email for your business.
Control file sharing
Review SharePoint and OneDrive sharing settings. External sharing can be useful, but it should be intentional. Old anonymous links, broad folder access and unmanaged guest users can create avoidable exposure.
Check devices and backups
Make sure business devices receive updates and use endpoint protection. Microsoft 365 is not a replacement for every backup scenario, so review how email, SharePoint, OneDrive and important business files would be restored after deletion or ransomware.
Good next step: schedule a Microsoft 365 security review before a problem appears. A short review can usually identify the highest-risk settings quickly.