A basic salad dressing is 1 part vinegar to 3 parts oil. After that, you can season with a little salt, pepper, and any other spices or ingredients you choose.
Whisk together, or add to a mason jar for easy storage and shake it up.
Here's a simple but flavourful one to start with:
1/4 cup of Apple Cider Vinegar
1/3 cup of Cold-pressed Olive Oil
2 tablespoons of Honey
2 tablespoons of Lemon Juice
1 clove of Garlic
Salt and Pepper to taste