What helped me was excavating my psyche through different methods with the conventional being psychological tests ranging to those more philosophically and spiritually based, books and such. I also meditated on what I used to love to do as a child before having traumatic experiences and wrote them down, painting a picture of who I am as a full person of good and bad traits. I think a lot of BPDs overidentify with their negative traits in a cycle that becomes a self fulfilling prophecy or which worsens the negatives when every person in the world is a mix of good and bad characteristics. You have to force yourself to identify more with the good in you as much as the bad in equal measure and do things that reinforce the traits you like about yourself. Monitor your self talk because that becomes your self image. If you have to take a walk around the block quietly saying what you like about yourself out loud, do it (not gonna lie, I did it today), and watch how the world responds in kind, by being kinder to you. I've always had the worst relationship with my mom and out of the blue she has been sending me really sweet and loving texts which was unheard of before. This makes me think my personal pet project is working.