Put aside time before your planned bedtime for winding down. Ideally this would be 1 – 2 hours. But put aside what you think is feasible for you. It's important to give this time the same status as your other commitments, so block it out in your calendar or diary.
Next, pick out activities that you enjoy, and that are relaxing in a passive way. Reading, going for a stroll or listening to music would all fit the bill.