The goal of a cool down is to settle your "state" (breathing, heart rate, nervous system) and possibly aid in the recovery process.

Some light stretches, and deep breathing exercises can really help you feel energised and ready for what's next in your day.

My approach to cooling down is fairly simple and free. There aren't many rules for cooling down so I normally suggest finding what feels good to you. My one recommendation is to pay attention to your level of tension and breathing. Think: "make my muscles melt and let go of tension". The breathing can help with that. 

~ Marianne