Adpted from Udi Barkan
The way for a tasty salad dressing, go through combining all the flavors - sour (vinegar, lemon, lime), sweet (any type of sugar), salty (salt, soy, fish sauce), fat (olive oil, tahini, avocado, Sesame oil) and some spiciness.
On this base you can add more flavors: mustard, garlic, ginger, herbs, spices and more.
Salad dressings have a tendency to separate (it's a mixture of liquid and fat), certainly if you prepare a large amount and keep in the fridge, but all you have to do is shake before serving and mix with the salad.