I've just started flying night freight and I've aked almost everyone I've met for tips.
Basically, everyone is different and has their own strategy. One thing that is clear though, is that it requires a lot of self disipline both before and after work. You really have to plan your rest and never be tempted, for instance on the first night, to try and make it through. I did that on some of my first observer trips and was fighting a losing battle by 6 am. I really don't remember much about the ride back to the hotel!
Once I'm down route I find it works best for me to sleep once straight after work and then again for a few hours immediately prior to check-in. Our pick up is often around 20.30 local and so it is hard to get to sleep at 5pm but just lying in bed and reading a book helps me store a few reserves for the night.
Luckily, my employer provides sleeping bunks for the pause between flights. Again, some people never use them as they prefer to stay awake, but I find the two hours or so that I can grab there enourmously helpful.
One last point, if you are a commuter. It is so tempting to jump into your car after a night's work and we've all been there, an hour down the motorway and suddenly it hits you. If you are lucky, you can feel it coming and pull over but I increasingly that as I get older, the tiredness comes on much more suddenly and you can have blacked out before you realise what has happened. I try to force myself to get a few hours before I set off home but this is easier said than done!
KT