Begin with a free movement around, without considering your mood or thoughts at all. Move your arms - lift them, rotate them, stretch them - as if warming up for a sporting endeavour. Include the legs. And so, until the whole body enters full physical dynamics of movements in different directions.
Don't think about anything - follow the body.
At some point, when the amplitude of the movement is filled with maximum activity, let your teacher or some of the observers clap their hands. This will be a signal to "FREEZE" instantly, no matter what position you found the signal.
Stop and try to sense your posture.
Start to imagine and justify the posture and then develop a movement - why are you standing that way, what could this posture mean, what am I doing right now, how can I finish this movement.
Suppose your frozen posture is stretched upwards, the arms are also stretched forward and upwards, the legs are in tension as if for a jump. This is an accidental position of the body that you did not even think you would get as a result.
Now you need to find a logical justification for this bodily position:
Maybe you threw a basketball in the basket; maybe you removed a suitcase from the trunk of the car roof; or maybe you are trying to pluck a fruit from a tree.
You can go on and on exploring possibilities. Choose the one you feel like the most and develop the movement of your choice.
Calm your mind and imagine for a moment - what physical activity in real life can be performed in this position. For what purpose would one take this position - what would be the reason?
Thus, your imagination gives purpose and direction to the movement, and it becomes justified, it turns into a logical action. Once you have found the story behind your "frozen" figure - UNFREEZE it - Develop the subsequent movement as a natural expression of a justified action.
Once you become familiar with this exercise, try to add a condition/quality to your justified action. For example, you are not just jumping to catch an apple, but your legs hurt, and you must jump many times to reach the apple, or you are freezing, or you are very hungry, you are enormously big, and so on. Think how the condition/quality is influencing your physical movement and the story behind the justified action.