Force diagrams must depict all the relevant forces that exist for an object in the given situation. You must think about what an object is doing, and consider if it is resting on something, or whether it is moving and make sure all the relevant forces are represented.

In the diagram below, a car is resting on the ground, both diagrams have the weight represented, but the diagram on the left is missing the normal reaction forces.

In the diagram below, a ball is falling down. As the ball is moving down, both diagrams have air resistance, but the diagram on the left is missing the weight force arrow.