The integration of Generative Artificial Intelligence (GenAI) in education has reshaped perspectives on teaching, highlighting the need for actionable strategies to support teachers in leveraging AI for instructional design. While existing research underscores the importance of AI literacy, limited guidance exists on how teachers can effectively incorporate GenAI into classroom practice. To address this gap, we propose a GenAI Social Role Framework, which defines three key roles for GenAI in the classroom: Connection Creator (Learn by Connecting), Simulated Learner (Learn by Teaching), and Evaluative Collaborator (Learn by Evaluating). This framework provides structured guidance on how teachers can integrate GenAI into classrooms to facilitate student engagement and deep learning. To illustrate its practical application, we present three real-world classroom scenarios in Beijing, China, demonstrating how GenAI can be embedded into different instructional contexts and classroom activities. These cases highlight the diverse ways in which teachers can design GenAI-supported learning activities, making GenAI a meaningful component of modern pedagogy. Building on educational practice, we further explore the challenges and opportunities in advancing GenAI applications in education and provide insights into future directions for research and implementation. The proposed framework offers a systematic approach to GenAI-enhanced teaching, equipping educators with practical strategies to harness AI for deeper learning experiences.