Just a little while ago I watch this Joe Rogan interview that he had with Sam Harris and his brother on mindfulness meditation where the focus of their attention is their breath. When their mind starts to wander away to different concerns they learn to recognize that they are getting lost in the thought stream and gently bring their attention back to their breath. Every time you do this you are slowly getting better at controlling the focus of your attention. It is like exercising a mental muscle. Also you start to become aware or an observer of your own thinking.
On a different note, I remember asking this real wise doctor once what is the best way to handle stress. He said the best way to handle stress is to leave it. I asked him what he meant and he said to me, " I wished I had my car here; I let you go out and wash it."