It may seem simple, but getting enough sleep is a big factor in reducing stress levels. It's recommended you get at least eight hours of sleep a night, but if you can manage nine or ten hours that's even better.
It's also important to wind down at least one hour before you intend to sleep, by reading a book, listening to music or meditating.
Have trouble sleeping? Check out these science-backed tips on how to sleep better from Headspace.