Article in English: Look at yourself in a mirror and time how long you can maintain eye contact without blinking.  You can also have a staring contest with someone else to test your ability. Having full command over your eye movements will help you maintain steady eye contact with the other person during the hypnosis. Do this by looking at a close object, like a pen or pencil and then a distant object in the room.  Hold the pencil close to your face. Focus on the pencil. Move from focusing on the pencil to an object that is further away, like a picture on the wall or a doorknob. Return to focusing on the pencil. Then focus on the distant object. Continue practicing this to improve your focus flexibility. This is your ability to see objects and movements on either side of you without having to turn your head. To improve this ability:  Sit in a busy scene outside on a sidewalk. Or sit in front of a TV or computer screen that is playing a busy scene. Try to look at the busy scene with your head turned to one side. Then, look at the scene with your head turned to other other side. Try to see as much of the scene as possible on either side. Make sure you practice from the left and from the right.

Summary in Vietnamese:
Cố gắng nhìn thật lâu không chớp mắt. Rèn luyện khả năng tập trung mắt. Tăng mức độ nhận biết ngoại vi.