Develop a Bedtime Ritual
Think of yourself as a newborn. Babies don’t know when to sleep and when to cry, which is why you develop all kinds of bedtime rituals for them. Your brain has forgotten the cues on when it’s supposed to shut off.
Therefore, you need to start an hour or two before bedtime with activities that remind the brain that its day is ending and it should get ready to stop thinking so much. Appropriate rituals include a warm bath, reading a book (that is not for work, or will stimulate you in any way), hot decaffeinated tea, saying prayers.