I’m always amazed at the percentage of folks who’ve never made their own vinaigrette, or salad dressing and prefer to buy ranch, blue cheese or thousand island at the grocery store.
Please visit my pantry series for what to have on hand. A basic vinaigrette is nothing more than acid, oil and seasoning. But there are thousands of combinations that you can tailor to your own tastes once you know the rules.
An acid can be lemon or orange juice, cider vinegar, balsamic, sherry or raspberry vinegar. The oil should be extra virgin olive oil if lemon, balsamic are used. Otherwise use something tasteless like canola. Some higher-end dressings include walnut or hazelnut oils, which must be refrigerated.
If you’re afraid the vinaigrette won’t bind use a binder such as Dijon mustard. Get a Pyrex measuring cup and a good whisk. See if you can find a sauce whisk, which is quite straight to get into the corners of a sauce pan, rather than a balloon whisk that you’d use for egg whites.
Next thing is level of acidity. Depending upon the amount of dressing you need, the French say one part acid to 3-4 parts oil. I do more of a 1:2 ratio because I like the acidity (which is why I buy Jim fat-free Ranch at the store).
Take one part acid. Salt and pepper to taste. Add a teaspoon or so of Dijon mustard and whisk to combine. Whisking all the time, slowly drizzle in oil (that’s why you’re using a measuring cup) until you have 2X the amount of acid. Dip in a spoon and taste. Are the seasonings right? Do you want more oil? Doctor it up. This is to your taste, not mine.
Even if it “breaks,” you’ll know because it will have separated. Add another tsp mustard and whisk and it should come back together.
After you master the basic version there are so many permutations out there that it’ll boggle the mind. I know, I was tested on them! Happy cooking!
Cooking with Dee 
Pretend you’re starting with 2Tbsp acid and probably 6 Tbsp oil, with 1 tsp mustard.
You add the salt to the acids (vinegar and mustard) so it dissolves, as it does not dissolve in oil.
If it REALLY breaks place mustard in a fresh measuring cup (an appropriate amount depending upon the amount of vinaigrette you’re making) and whisk the broken sauce into the mustard, adding it slowly.
When dressing a salad, each leaf should be lightly coated. There should be no dry leaves once you’ve carefully tossed the leaves with tongs (or your meticulously clean hands) nor should the salad be swimming in dressing. You can always top the container with plastic, refrigerate and use it tomorrow. Dee