Gently grip the skin just below the penis head on the underside; place it between the thumb and index finger, and start rubbing, almost like you're snapping your fingers with just your index finger. You won't feel anything until you're almost about to ejaculate.
Start masturbating normally, paying close attention to the penis head. When you feel you're about to ejaculate, slow down and switch to the Skin Flick technique and continue. With this variation you usually don't have as strong an orgasm as when you use the Skin Flick method all the way from the start.