I've been thrifting for as long as I can remember, here are some things I've learned.
There are 3 levels of thrifting. Bins, donation centers, and boutiques. Bins are the hardest to thrift from and boutiques are the easiest. Bins are also the cheapest and boutiques are the most expensive.
When thrifting in bins, its every man for himself. The bins are dirty, nothing is sorted, and often times the clothes are in poor state. When going bin diving you should bring gloves and hand sanitizer. Bins require patience, if you want something good you'll have to sort for a while. Its also a good idea to bring a friend and work together. You pay by weight in bins most often.
Then there are donation centers, like goodwill. Goodwill sorts its clothes and prices each item individually. The clothes are typically clean but there is no promises.
Boutiques are the most expensive thrift. Boutiques hand pick each item and clean them individually. Boutiques typically have more expensive clothes and you are most likely to find designer/ vintage clothing there.
The best times to thrift are monday tuesday wednesday, in the early mornings. This is when thrift stores restock and put new clothes out. If You want to find out the exact day they put clothes out you can look up the store phone number and ask. You want to get to the thrift before the other thrift girlies and the old ladies.
When thrifting make sure to clear out a few hours because it takes time and I personally always lose track of time.