Recent trends in Extended Reality technologies, including Virtual Reality and Mixed Reality, indicate that the future infrastructure will be distributed and collaborative, where end-users as well as experts meet, communicate, learn, interact with each other, and coordinate their activities using a globally shared network and meditated environments. The integration of new display devices has largely changed how users interact with the system and how those activities, in turn, change their perception and experience. Although a considerable amount of research has already been done in the fields of computer-supported collaborative work, human-computer interaction, extended reality, cognitive psychology, perception, and social sciences, there is still no in-depth review to determine the current state of research on multiple-user-experience-centred design at the intersection of these domains. This paper aims to present an overview of research work on coexperience and analyses important aspects of human factors to be considered to enhance collaboration and user interaction in collaborative extended reality platforms, including: (i) presence-related factors, (ii) group dynamics and collaboration patterns, (iii) avatars and embodied agents, (iv) nonverbal communication, (v) group size, and (vi) awareness of physical and virtual world. Finally, this paper identifies research gaps and suggests key directions for future research considerations in this multidisciplinary research domain.