Sleep. It's a matter of trial and error, really. Everyone's different.
For my first night ride, I took the day off work, had a little lie-in and tried to take a short nap in the afternoon but found this doesn't really work for me -- I'm too excited to sleep 'extra'! So now I just take it as it comes and deal with the aftermath.
Some people power through on willpower. It doesn't help to be coming into it with a sleep deficit though so do try and keep to regular hours for 4-5 days beforehand if you can i.e. not burning the candle at both ends. Some people find they're fine on the ride itself but crash as soon as it's over -- in fact, I'd hazard a guess that this response is the most common. Peruse FNRttC threads for pics and there's always one of Dellzeqq asleep over breakfast. Me, I go doolallly on the train home. Some people manage just fine til they get home then crash til Sunday morning (you'll see their ride reports don't turn up here until Sunday afternoon). Flying Dodo does just fine the whole day, even does DIY etc, then drifts off around 8pm in front of the telly -- I don't know if he's always been that way, he's been doing night rides for years so maybe this nearly normal aftermath has evolved.
The only constant here is the accepted wisdom that you must not attempt to operate a motorised vehicle until you are fully recovered, i.e. after you've got home and got whatever sleep your body says you need. In an actual bed. (Catnapping in a bus stop -- or in your car before setting off - does not qualify.)
In other words, don't totally wear yourself out in the days leading up to the night ride. Beyond that, you'll have to learn what your body teaches you. But you'll almost certainly get through the night ride itself just fine -- it's how you feel afterwards that is the Great Unknown.
Hope this helps. I'm sure others will pitch in as well...