The first principle in running effective meetings is:

A) assigning roles.
B) inviting the right people.
C) clarifying the purpose.
D) picking the most appropriate communication mechanism.

Clarifying the purpose of the meeting is essential in running an effective meeting. It sets clear expectations for participants and helps keep the meeting on track. Assigning roles, inviting the right people, and picking the most appropriate communication mechanism are also important, but they are secondary to clarifying the purpose.