If you see a few thrift stores recommended more than once on different websites - visit those places first.
Message local businesses in the area where they recommend. Check out online reviews. Check their social media.
Call thrift shops you plan to visit & ask them when they restock new items. Mark your calendar to go those days (or the next day) to get the best stuff!
Want a vintage leather jacket? Or a wool overcoat? Shop those "winter" items in the summer when demand is low.
If you want vintage clothing but visit a popular thrift store that specializes in vintage toys, you will be disappointed. What type of thrift stores will you visit first?