There are several key factors that contribute to effective groups and teams. Groups are classified based on how they are formed (planned or emergent) and their purpose (primary, secondary, task-oriented). Successful teams and groups have clearly defined goals, the right composition and skills among members, established norms, and foundations like trust, leadership, and decision-making. The stages of group development include forming, storming, norming, performing, and adjourning. Group dynamics and performance are influenced by characteristics such as size, composition, cohesiveness, and norms.