I fly to NGO which is 14 hrs from DTW about 6 times per year. Here's my approach:
1. Eat well before departing and have the first meal as a snack.
2. No alcohol. I won't sleep well as I dry out and have to get up to go. Water, ginger ale, tea. Boring but it works.
3. Stay awake until about normal bed time. Sleep for awhile.
4. Watch a movie or show.
5. Go back to sleep and if I can't put on a garbage movie, of which DL has many to choose from. Puts me down to sleep.
6. At this point, we are about 4-5 hours away. Try another movie or tv shows for awhile and maybe a cat nap.
7. Breakfast. We will be there in an hour so stay awake.
8. Done.
The keys to a good flight to me are 1, 2, and 5.