I've had a problem with intermittently poor sleep for ages, but what's really helped a lot is giving up alcohol.
Not that I drank that much, but part of my weight loss and fitness drive for 2018 has been to keep off the stuff completely (for an as-yet undetermined length of time), and I haven't had a drop since before the New Year. My sleep has improved greatly - I'm getting off to sleep quite quickly, only rarely suffering any restlessness, and I get up right away in the morning without feeling the need to doze for ages first.