Hyozaemon, a long-established chopsticks maker in Obama, Fukui Prefecture, tells us how to hold chopsticks properly.
Hold chopsticks about two-thirds from the end. The upper chopstick should be held by grasping it between the thumb and index finger, and support the chopstick underneath using the middle finger. The lower chopstick should be held in place between the base of the thumb and the index finger and pinky. The middle finger should rest between the upper and lower chopsticks.
When using chopsticks, only the upper chopstick should be moved. Imagine moving the chopstick by pushing it up with the middle finger and pulling it down with the index finger.