Snake Arms
If you are having trouble with this move, try it from a different approach. Instead of focussing on which parts of the arm lift first, focus on the shoulders. If you are right-handed, start with your right shoulder, if you are left-handed start with your left. Begin by simply rolling your shoulder forward, up, back, and down a few times. Now simply continue to roll your shoulder and put your arm out, 90 degrees from your body, parallel to the floor. Notice how your elbow and wrist naturally respond to rolling your shoulder. When you push your shoulder forward, your elbow comes up. Roll your shoulder up and back, and your elbow will naturally drop and your wrist will come up. Practice just allowing this flow a few times before exaggerating the movement: roll shoulder forward, elbow comes up. Roll shoulder up, wrist comes up. Roll shoulder back and down, fingers flick up.
Imagine holding a delicate jewel between your thumb and middle finger throughout the exercise to give the movement an extra grace.