Here we see the setup. The lemons have been squeezed and the liquor (in this case Canadian Club) is going in the measuring glass. Dad usually used two and a half ounces of whiskey for each drink along with one lemon and two to three teaspoons of sugar.
Now we are shaking. Concentration is key in this step.
And now the finish. The glasses have been set out and the strainer stands ready. Notice the look of satisfaction and anticipation on Dad's face. Makes me kind of thirsty just looking at this scene.