Just like defensive swimming, keep your feet on the surface to avoid entrapment. Arching the back can help keep your head on the surface and ride a bit above the water.
You can support your head with your hands to keep it up and out of the water. This also leaves the hands in an easy to see area for the shore teams so they will quickly notice when you are about to give a signal. Don't forget to keep your elbows tucked in close to your body so they will not bang into anything.
This is a fun drill. We typically have the students try a number of positions to see the effects on their bodies. When done, they simply pull the quick release and swim to shore.