Poor boundaries begins with the belief that your experience (wants, needs, expression, feelings) are somehow wrong.
If you start with that (incorrect) sentiment, everything after that tends to be an apology, avoidance or discount of your lived reality
“I’m not really scared, I’m ok”
“Yes you can have that thing (that makes my belly tightened as I think of giving it away.. my belly really shouldn’t be tightening and I wish it wouldn’t)”
If we start instead with the presumption that your experience is valid, your needs important and your feelings precious and to be treated with honour and tenderness …
There’s no reason to over ride your experience or needs in favour of someone else’s*. No reason to say yes when you mean no, no reason to discount You in favour of someone else.
(*Unless we’re talking about parenting a dependant child)
If we start from that place, everything is an opportunity for honest sharing of your internal world. And when you honestly share your internal world without belittling, or denying it, the world will show you who is to be trusted and who isn’t.
You will naturally move away from the people who disrespect or deny your experience, and naturally move towards those who have space, time and care for you. Because they behave like they love you having boundaries, and that makes for healthy relationship.