In a salad bowl, combine the vinegar, 1/2 teaspoon salt, and the pepper. Whisk until the salt dissolves. Once the salt has dissolved, continue whisking while you slowly drizzle in the olive oil until the mixture becomes thick and creamy. Adjust the seasoning to taste. Just before serving, add the greens and toss to coat with the dressing.
The classic vinaigrette ratio combines 1 part vinegar to 3 parts oil. One teaspoon of Dijon mustard is often added, too. Your preference may call for a different mixing ratio. Other oils and vinegars will alter the taste and combination ratio as well.