I do equal parts balsamic vinegar and extra virgin olive oil (usually a small portion for me where I have left overs is 1/8 C of each) . Then I add a couple shakes of garlic salt and pepper flakes to taste. You can make as much or as little as you want just start with equal parts oil and vinegar.
Next I whisk it all together so it’s well combined and taste it. Sometimes I end up adding a little more salt or more balsamic or vinegar depending on how I feel that day. You can throw in any other herbs or lemon juice for a little change. But that’s the basic recipe with how I make it most of the time. I just throw the left overs into a container. Even better than that if you have a small jar just throw all the ingredients in that and shake like crazy (I couldn’t find my small jar this time).