Knowing the basic components of a vinaigrette salad dressing will allow you to make a number of variations to go with different types of salads.
In a small bowl, use a whisk or fork to combine the oil, vinegar, dijon mustard, salt and pepper (to taste) and any optional ingredients you want. With garlic or shallots, you really don't need both--just choose one or the other for extra flavor. Minced herbs can be added alone or in addition to the garlic or shallots.
There are many different types of vinegars that will work well in this recipe: apple cider vinegar, white wine vinegar, red wine vinegar, and balsamic vinegar are all excellent choices. The proportions listed above work great with apple cider vinegar but may need slight adjustment for other vinegars depending on how strong their flavor is.
If you have a salad dressing shaker or a plastic container or jar with a tight-fitting lid, you can also combine the ingredients by pouring them all into the container, fastening the lid on tight, and shaking thoroughly.
After mixing, taste test your dressing to see if it needs more or less salt, pepper, or vinegar. If the mixture is too salty, vinegary, or peppery, add more olive oil. If the mixture tastes too oily, add more vinegar.
Add the dressing to the salad immediately after shaking it since oil and vinegar tend to separate. However, don't add the dressing to the salad more than a couple minutes before eating it or your lettuce may get soggy.