How do you make better friends?

I’m reeling from an experience where I tried reconnecting with an ex-friend. I assumed that they had grown and changed and wanted to come to a place of understanding but I assumed wrong. I keep thinking people have the same intentions as I do and I get into situations where I am yet again blindsided that they don’t. I need to remember how to not be so open but I don’t.

What tips do you have for having better emotional intelligence and boundaries? Especially for people who aren’t overtly terrible?