Trick to making perfect egg ribbons?

I can't speak to your specific recipe, but I worked in a Chinese take-out restaurant for a few years, but that was a ways back....if I remember correctly, the process was extremely simple.

1. Start with a broth of hot water, white vinegar, salt and a drop or two of yellow food coloring (ancient Chinese secret - food coloring)
2. Get it nice and hot and add a small amount of cornstarch slurry, whisk and wait for it to thicken.
3. Meanwhile, scramble some eggs, just like normal. Nothing special. We used a fork and scrambled the eggs in a take-out soup container.
4. Pour the eggs into the broth at a steady rate while stirring the broth at a medium and consistent speed (roughly one rev/sec).

And that was it. As far as specific technique? I can't recall anything that really stands out. Like I mentioned, we used a take-out soup container and a fork to scramble the eggs, and cut a hole in the top to pour them. I suppose if you want to get really specific, we used a box cutter to make a triangular hole, roughly 3/4 inch per side. The soup was cooked in a round-bottomed wok, and stirred with what Google is telling me is called a hand-spoon - imagine a one-cup ladle, except bend the cup so it's more or less parallel to the handle.

Hope this helps. If you'd like any more information I'll try and see what I can drag out of the back of my dusty memory - it was about six-seven years ago, but I might be able to persuade my feeble old mind to provide some more details.

Vinegar is a good part of recipe, however adding a little water to your scrambled egg is another trick. And after the broth with cornstarch and water has been whisked separately, then added to slow boil or simmer to your broth and simmered to marry well for 1-2 mins, turn off heat. Whisk your eggs in a pouring measuring glass with a fork. With same fork, start stirring a continuous swirling stir (right to left or left to right does not matter, but must be in same direction). Slowly and in a small stream, pour the egg into the broth while swirl stirring.

Here's a technique I found in a recipe for Hot and Sour Soup: Beat together egg with 1/2 teaspoon cornstarch. Bring soup to a boil, reduce to a bare simmer, and slowly pour the egg into the soup in a thin steady stream. Let egg set for 15 seconds, then stir gently to incorporate.