Avoid caffeine after 3 pm (including caffeine in fizzy drinks, Lucozade etc).
Avoid heavy meals and strenuous exercise within two hours of bedtime.
Alcohol intake results in worsening sleep apnoea and rebound hyper-alertness in the middle of the night when the effect wears off. Limit intake as much as possible.
Avoid smoking 2 hours before bedtime.
Avoid using electronic devices in bed (TV, Kindle, laptop, phone etc).
Keep the bedroom dark (with black out curtains, if necessary) and at the optimum temperature (check heaters are not on maximum, no cold drafts from open windows etc)