Where should I begin implementing Zero Trust in a small Microsoft 365 tenant?

Start with identity rather than trying to tackle every Zero Trust pillar at once. For internal users, enable MFA, block legacy authentication, and require joined or compliant devices for sensitive applications. For guests, keep them limited to guest accounts and grant only the SharePoint access they actually need. A separate Conditional Access policy for guests can prevent unmanaged devices from accessing more of the tenant than intended. The easiest wins are making MFA mandatory and eliminating legacy authentication. The biggest challenge is usually guest access: security policies that work for employees can unintentionally block a partner trying to open one shared library from a home computer. Treat the assessment as a roadmap, not a requirement to implement the entire maturity model immediately. A sensible first phase is sign-in protection and guest scoping, followed by device controls and broader data protections.

Don’t overlook devices that aren’t traditional user computers. Printers, copiers, scanners, and similar equipment are often treated as trusted devices but may not support modern authentication or compliance checks. If they handle documents or connect to Microsoft 365 resources, identify their access paths early and plan an appropriate management or intermediary solution rather than discovering the issue during enforcement.

Use the assessment and maturity model to identify gaps, but turn the results into small, testable phases. Begin with an inventory of identities, applications, guests, and sensitive SharePoint data. Then pilot Conditional Access with a small group, use report-only mode where possible, and make sure you have emergency access accounts before enforcing policies broadly. This helps reveal exceptions without locking everyone out.