When developing the project management plan, a project manager relies significantly on certain interpersonal skills. Conflict management is crucial as it helps in resolving disputes and ensuring smooth collaboration among team members. Facilitation is important to guide discussions and ensure productive meetings and group sessions. Meeting management is essential for organizing and conducting meetings effectively to make sure that all aspects of the project are discussed and communicated properly. Interviews and focus groups, while helpful, are more specific techniques rather than broad interpersonal skills needed in the development of the overall management plan.