The traditional perimeter-based security model has proven insufficient against modern cyber threats that exploit trusted internal connections and lateral movement within enterprise networks. Zero Trust Architecture (ZTA) operates on the principle of 'never trust, always verify,' treating every access request as potentially hostile regardless of its origin. This paper presents a structured, step-by-step methodology for IT teams to design and deploy a Zero Trust security framework. The approach covers identity and access management, micro-segmentation, continuous monitoring, and policy enforcement across hybrid environments. Case analysis from enterprise deployments demonstrates measurable reductions in breach frequency and detection time. The paper also addresses common obstacles including legacy system integration, user resistance, and budget constraints, offering practical mitigation strategies for each.