Choosing the flight time (if options are available) is important for me. For flights to the US (especially West coast), I try to take the late afternoon ones. I have a bit of a nap on the plane but you arrive early evening, so despite your long day, it’s not that far from bed time. Coming home, I try to take a day flight, or if not, at least one that is a bit longer from the east coast (like MIA). I try to avoid getting to London too early in the morning. Going to Asia, preferably 18:00ish departure from London gets you there lunchtime/early afternoon. Those midday departures are a bit brutal, especially if not connecting as it’s a long day ahead. Coming home I try for a day flight, but if not then the late ones are not too bad as they are long enough to sleep.
Like others have said, once on board I try to work on destination time. Going east that means getting my head down fairly soon after dinner. I try not to sleep right to the latter part of the flight if possible. Going west, I’ll have a nap after the meal and then a coffee with the second service to keep me a bit more awake, especially if it’s not an evening arrival time. On the late night departures from Asia, I’ll try to stay awake for a few hours and then sleep through to morning.
Again, I try not to stuff my face and will drink no, or very little alcohol and try to sleep according to destination time. I get very dehydrated anyway, so I will always take a large bottle of water on board. If I can avoid a 777 or 747 I will, as the newer planes really help.
I do use a mild sleeping tablet sometimes. Sleepeaze – available over the counter from Boot’s – is basically just Benadryl, so nothing scary. I will use it to help me get to sleep in Asia and it prevents me from waking up too early in the US. I usually only need it for the first night or so. On those overnight departures to Asia they help me get to sleep on the plane when it’s still early evening in Europe.