Plan" is really a two-step process. The first step consists of identifying and defining a problem existing within a process. The second step involves analysis of this problem. During these two processes, many tools and steps will need to take place including:
Determining the root cause of the problem.
Determining the interventions necessary to correct the problem.
Determining what the expected outcomes are.
Determining who the responsible parties will be for the improvement of the problem.
Scheduling the steps of the correction.
Planning for resources.