Sleep is a major power multiplier for mental and physical performance. My experiments revealed (anecdotally, this isn't hard science yall) that in this order I received the most powerful deep sleep from the following and best when cocktailed.

• Cold exposure
  10-20 min 50F bath before bed, and an ice pack on the upper back for 30 minutes seemed to be about 20-30% as effective as cold exposure alternative to baths
• Carb restriction
  Especially effective if no or very small amounts of carbs are consumed 5 hours before sleep
• Go to bed on an empty stomach or small amounts of fat/protein
• Physical exercise 3 hours or more before bed
• Vitamin D3, niacin, and omega -3 supplementation at bedtime
• A successful day
  Enumerate the successes and completed tasks for the day before bed

I would be remiss to leave out prayer. It's definitely a powerful path to a peaceful mind. It's hard to classify its impact, since sometimes prayer gives me a calm mind, and sometimes makes me think of things in a way that makes me want to do things besides sleep.