While a 1-to-2 acid-to-oil ratio is common for vinaigrette, shifting it to 1-to-1½ yields a dressing with a brighter flavor and fewer calories. That means for every ½ cup of acid, such as vinegar or lemon juice, use 3/4 cup of oil. Here's a good all-purpose take on the formula.
To make ahead
Refrigerate for up to 1 week. Shake before using.