Don't leave people in charge of the test plan who have never done anything resembling a test plan before; This is vital, they will learn nothing from it and the test will fail.
This issue includes all areas of the plan. Here are some examples:
Selecting features to be tested and not tested.
Setting overall strategy for this level of plan.
Ensuring all required elements are in place for testing.
Providing for resolution of scheduling conflicts, especially, if testing is done on the production system.
Who provides the required training?
Who makes the critical go/no go decisions for items not covered in the test plans?