Traditional French vinaigrette is made with 3 parts oil and 1 part vinegar. I prefer it (and so do my arteries) with less oil and more vinegar. And I usually add a little bit of Dijon mustard because for some reason, it helps the rest of the ingredients emulsify (combine and thicken) and stay together instead of separating so that you have an oil slick floating on top of the vinegar.
1/2 cup red or white wine vinegar
1/4 teaspoon salt
1/8 teaspoon pepper
1 tablespoon chopped fresh herbs, or 1 teaspoon dried
1 teaspoon Dijon mustard
1/2 cup olive oil
Put the vinegar, salt, pepper, herbs and mustard in a small bowl. Gradually pour in the olive oil, stirring constantly with a wire whisk, until the ingredients are well-combined.
You can also use this basic recipe to make a lemon or lime vinaigrette by substituting lemon or lime juice for the vinegar.