I have an ongoing list of things I need/ want that I watch for at thrift stores (I'm also not opposed to buying them on clearance). My list includes some kitchen things, the sizes Gideon needs in different types of clothes, yarn and other craft supplies, and many books. I am building a collection for Gideon of books I loved as a kid and from authors/ illustrators that I like. I'm also building a collection of chapter books for him.
I'm by no means a pro thrift shopper. I know there are people who thrift and then sell the treasures they find online and make money. I do have some tips for the basic for family thrift shopper though!
1. Keep an ongoing list of things you need or want. I used to keep a note on my phone until my list started getting too long and then I switched to a small notebook I keep in my purse.
2. Find out when or if the thrift store has half or or sale days. Goodwill does a certain color tag starting on Sundays for the week. A local thrift store I go to does certain types of items every few days- one day clothes are 25% off, another day books are 35% off, etc.
3. Don't expect to find everything (or even anything) each time. It's not a grocery store and there are no guarantees.
4. Go often and browse. You don't have to be there for hours. Just a lunch break or a few minutes while the baby is happy will work. Find out if the thrift store does a specific stocking day or time so you can go and get first look at things.
5. Don't buy things you don't need! Just because it's cheaper than new, if it's just going to collect dust in your house, it's no good to you!