The feet should screw into the floor during the press to add leg drive to the lift; but it is imperative that this not result in lifting the hips off of the bench. (onnit.com)
Lift hips up as high as possible, forming a straight line from head to heels. (mindbodygreen.com)
Keep the arms strong and supportive while you work on lifting the hips toward the sky. (mindbodygreen.com)