Action plans are, in effect, roadmaps to achieve goals. They should contain a description of the improvement goal, names of people on the team, steps to be taken, names assigned to the steps, and due dates for steps.
Some action plans are simple in their layout. Others add in additional features, such as a graphical timeline, a synopsis of the current situation, graphics that show completions progress, and other bells and whistles. Advanced action plans use Work Breakdown Structure (WBS), a project management tool, to break projects down into discrete work elements.
Regardless of how they look, action plans are support tools used to keep a project on track.
Keep in mind, though, action plans are only useful if they are followed, regardless of how good they look. Someone should be responsible for tracking and updating the action plan. Generally, this person will be the project owner. Most importantly, it should be someone who can keep the project on track, either through authority, or through natural leadership and finesse in dealing with people.