Assuming you're in economy - does the airline have seatback on-demand IFE? If they haven't, take a laptop and load it with films (a tablet is superb for this). Makes sure it's fully charged. Kindles are also great if you're a reader.
Actually, you might be better off without seatback screens. Last time I flew economy long-haul was San Francisco - Frankfurt and the fecking sod behind me was jabbing at the screen for hours. He stopped after I gave him a glaring look after about 7 hours.
For sleeping - invest in a little travel pack. I got one for a few dollars in San Francisco before that flight, contained a decent inflatable neck pillow, and earplugs and eye mask (which I already had). Makes sleeping much easier. Take your shoes off and an extra pair of socks to keep your feet warm. Oh and if it's an overnight flight and you're losing hours (eastbound transatlantic, for example), try and sleep as soon and as much as possible. I normally try and have some consideration and don't recline my seats much, but on long-haul it's a must.
Truth is, long-haul economy travel is crap. You'll be bored and frustrated after a couple of hours and won't sleep well. There will always be a whingey brat keeping you awake and the PA system will 'BONG' every time you're drifting off.
Of course, if you're business class don't worry and just enjoy! In my job I tend to get Business Class and it's an absolute world of difference. Plus the cabin crew chuck loads of booze down your neck to try and get you to sleep.
