I forget exactly when and how Rebecca cracked the code on making authentic (read: Hidden Valley) ranch dressing at home. The secret is so funny: chicken bouillon powder!
I make this on the fly and don't measure a thing, but I'll guess at the measurements to give you a helping hand.
3/4 cup regular yogurt (use Greek yogurt if you want a dip)
1/2 tsp. chicken bouillon powder
pinches of dried herbs such as basil, oregano, dill, thyme, or marjoram
sprinkle of garlic powder or minced garlic clove
Taste and add more bouillon powder if needed. If you have a bare pantry for whatever valid reason, just use salt. Possibly add pepper. Play around! How many variations on the Hidden Valley Ranch flavor are there? As many as you want to make!
Probably the flavor would deepen if you had time to let the ranch dressing sit a little bit, but I've made it and served it right away in the supper rush, and it was delicious. See, I also grabbed my camera in the supper rush to present you with photographic evidence of this dressing. It also keeps just fine in the fridge for a week or so.