My mind sometimes has a hard time coming to rest, letting go, during samatha meditation. It can be about everything from thoughts about people, what I should eat, but most often reactions to situations I have found myself in or how I can solve problems both private and at work. Some time ago during meditation I had the feeling, the experience that I was sitting with a bunch of helium-filled balloons in my hands. Each balloon represented a thought, a problem, a person I have a problem with etc. I gradually began to let go of the balloon as the conceptual mind stuck in one of these representations. It went away and I could mentally go back to single pointed meditation. When negative, non-vertius, thoughts appear, I place them in a balloon and then puncture it. It helps me stay focused, come back to samatha meditation, when my mind is too excited.
Maybe it can help some of you who also sometimes have a hard time letting go. Just be careful not to fall into the trap of focusing on balloons 🙂 Been there, done that 🙂