How Do I Stop My Thoughts?

Hello, I have a question about working with thoughts. I find my thoughts run completely wild, and I have little conscious control of my thinking. My current strategy to deal with these thoughts is to let them run as wild as they like. I have thoughts about whatever makes me most uncomfortable running automatically, coming up as images and words. How can I clean up this thought space?
I would also like to be able to use my thoughts only when necessary (not having them constantly be running on automatic), is this a skill that is possible to learn?