Your Basic Vinaigrette

A little more oil than acid... That's my basic rule of thumb. 

So, 

1/3 cup vinegar (red wine, white wine, balsamic)

1/2 cup EVOO (or other good oil)

S & P to taste

You can put the vinegar in a bowl, add S&P and whisk in EVOO to emulsify (make it hold together) OR you can put it all in a sealed container and shake the heck out of it too. I find this to be much easier. 

Now that you know that basics, you can play with add ins. Like subbing in fresh squeezed lemon for the "acid" to make a Lemon Vinaigrette. Mix in fresh herbs like oregano and parsley for a Greek vinaigrette. A small dollop of Dijon mustard is a great emulsifier too; I add it to most vinaigrettes I make. 

When I cook, I tend to guestimate more than measure. Don't be afraid to eye-ball it. Don't be afraid to change a recipe to suit your taste better either.