When you notice that your trailer has lost traction and is going into a skid, you should _________.

Stop using the brake. Release the brakes to get traction back. Do not use the trailer hand brake (if you have one) to straighten out the rig. This is the wrong thing to do because the brakes on the trailer wheels caused the skid in the first place. Once the trailer wheels grip the road again, the trailer will start to follow the tractor and straighten out.