Securing your Microsoft 365 environment involves several best practices. First, enable multi-factor authentication (MFA) for all users to add an extra layer of protection. Regularly review and update user permissions, adhering to the principle of least privilege. Utilize advanced threat protection (ATP) to safeguard against phishing and malware attacks. Implement data loss prevention (DLP) policies to protect sensitive information. Monitor user activity with Azure AD logs and set up alerts for suspicious behavior. Regularly train employees on security awareness to minimize human errors. Finally, keep all software and security patches up to date to mitigate vulnerabilities and ensure compliance.