You really have to be in the mood for this type of shopping. You can't be angry, hungover or hungry - I've tried, and it never works. My secret is to NOT carry a bag or anything heavy. You must have both arms working, because there's so much digging to do. Just crumple up a wad of cash and a good lip gloss in the back pocket of your jeans and head to your nearest thrift shop.
Because fashion trends traditionally get recycled, you can reliably predict that current trends pay homage to some aspect of fashion from 20 years ago. In the 1990s bell bottoms were made popular again when everyone vowed never to revisit the 70's. And recently, high-waisted denim is all the rage just when it was thought that mom jeans were a thing of the 80's. The coolest thing about thrift stores is that fashion from so many decades are always available, so you never have to spend a fortune to have fun with trends while still being frugal and unique.