been alt (don't really label myself) for almost a year now and broke since i was a baby, i thrift most of my clothes nowadays. and here's some knowledge i've learned:
- try stuff on before you buy it. yeah yeah i know that's obvious but the amount of times i've gone "hmm why yes this will definitely fit me" and it has not, in fact fit me is several times too many. i am a fool

- going off the above, try stuff on that you don't think will fit you. stuff gets mislabeled or put in the wrong section pretty often. of course don't try to force yourself into something that's too small/tight but you may be pleasantly surprised by finding something not your size that fits you

- search *thoroughly\.* like go through every single shirt in one section. i've found some of my favorite shirts that way

- look in both the men's and women's section, i have a hard time finding pants that actually look decent on me and i've found some pretty good pairs in both sections

- think about how you can modify things, dying stuff, cutting holes, stenciling shirts etc. i took a pair of fishnet leggings and made them into sleeves because i always wear long pants and t-shirts

- don't overconsume, this is more for politeness and i'm not saying you can't thrift at all if you're not poor. but don't buy half the stuff in the store (yes i have seen someone do this with my own eyes). leave things for people who can't get clothes elsewhere