Make a to-do-list.

The act of writing down uncompleted tasks can help you stop worrying about work at night. Keep a journal where you write down your thoughts and feelings, rather than just thinking about them. Other effective ways to help combat negative thoughts at night is being physically active during the day and practicing meditation. Ideally you incorporate all three into your routine. 

Why it helps:
Exercising and keeping a journal both help process emotions and reduce stress and anxiety. This has a positive impact on your sleep quality.