I typically use Lee Kum Kee's Premium Soy Sauce, which has a little added sugar to balance out the saltiness of the soy sauce. If you taste the dipping sauce and think it is too salty, dilute it with 2 or 3 tablespoons of filtered water and taste. You can also add 1/2 teaspoon of sugar to see if it balances out the flavors more.
SUBSTITUTION: You can substitute Zhenjiang vinegar with rice vinegar. Rice vinegar is much more tangy than Zhenjiang vinegar, so I would start with 2 tablespoons or rice vinegar and add more if you want the sauce to be tangier.
I like using a microplane zester to grate my garlic and ginger. If you don't have one, you can mince both the garlic and ginger.