Mindfulness tips to stop ruminating?

I’m in therapy and DBT learning skills which is helpful, but right now they are more tailored to crisis and distress tolerance. I had a best friend breakup. Awful and cruel things were said to me, and I’m blaming myself despite knowing for the most part she’s to blame. Anyway, as I’m doing in this post, I keep ruminating. I try to use my mindfulness skills and bring myself back to the present but my brain is fighting against me and seconds later it pops in my head again.

What are some practical tips to finding ruminating and intrusive thoughts through mindfulness?