How do you tell when a brand has real sustainability initiatives and is not just greenwashing?

I’ve been trying to shop more intentionally lately, but it’s hard to tell what’s actually sustainable versus just well marketed. I’m curious how people here evaluate what is a "safe" brand to shop from an environmental perspective, especially around materials and transparency. I know the most sustainable way to buy clothing is to thrift, but I do still want to purchase things new sometimes and I want to have a few go-tos that I know I can trust.