I've had Cognitive Behavioural Therapy over a number of years ago for depression, which has helped in how I look at things, instead of just black/white thinking.
I resort to having some top-up therapy sessions, every so often when on edge, and feeling my moods are a bit out of control or very low/high. A befriender, Mind or Samaritans can help, and sometimes a good GP just by listening.
I am on anti-anxiety meds, which I suppose help. I certainly notice, when I don't take them regularly.
Mindfulness or going to yoga, massage all help to relax a bit. Exercise is also recommended, if you are into that.
But, most of all, coming to accept yourself as being just okay, will help. Self-care and positive thinking are easy enough when in a good place. But, knowing when to ask for a bit of help or hand-holding is essential.
The goal is to remain a functioning person with BPD, and be fairly comfortable with it.
Hope some of this info helps you.