I suggest mindful meditation. With mindful meditation you don't attempt to control your thoughts, rather you accept the thoughts as they come and view them objectively. This link gives a decent description of what to do to get started:
Five Steps to Mindfulness | Mindful
I find a quiet spot and sit in a chair, I set my phone timer for 10 minutes and I focus on following my breathing in and out. My mind wanders, but I bring it back to my breathing, focusing and following my breath in and out. Each time my mind wanders, I bring it back to my breathing. I don't attempt to do anything other than be aware of my breathing as it is happening. Mindfulness is all about being focused on what is happening in the present moment, and focusing on my breath keeps me in the present moment and away from obsessing about the past or the future.