Drink lots of double strength coffee! Try to stay awake as long as possible so when it's time to sleep it won't be a problem. If you can't sleep just relax with a movie or music.
It depends on what sailing you are doing solo ? 2 up? 3 up? Full crew? Racing? Delivery?
Keep warm.
Wear a beanie.
Use a head lamp.
Have a good meal before sundown.
Enjoy the sound and feel of the ocean at night and the stars above. I love it.
It's a night cruise, just 2 pob, about 20-25nm. It will be close to full moon so that'll be cool. . Thanks for the tips.
If it's only 20-25nm you can push through the night without sleeping, but in general I'd encourage you to set up watches so someone is always alert. For example, I just did a 150nm overnight race and we set it up so had one watch awake from 10pm to 2am and the other from 2am to 6am. Other than those mandatory watches, everyone could sleep (or not) as they liked. There are lots of ways you can organise watches, but the key thing is to make sure someone on the helm is always alert.
Try not to use white lights too much , as those bright torch lights and cabin lights will affect your night vision for other distant small red green and white navigation lights .
While under sail , You should only run either your masthead tri colur or your nav lights fitted to your boat down lower . ( port ,starboard and stern lights )
Enjoy the disorientation !!! 
and the fizzing water !
If there is any risk of falling asleep , I have a kitchen timer in the pilot house . All is clear, viz. or radar , you have at least 15 min. before a collision situation with a ship. Set the timer and have a nap. Awake , do a reccy and grab another 15 min. I have used this for many years but would not use it coastal because small boats and plastic boats may not show on radar. There is also coffee and Red Bull but after 48 hrs it doesn't work !!
Used to sail two up quite a bit at night...we found it worked well if one person had a nap to about 9-10pm then we'd commence two hour about watches until morning. Two hours doesn't sound long but night watches can be boring and tiring and a two hour nap is usually enough to keep most people feeling fairly rested.
We'd always do a bit of a hand over when coming on/off watch i.e. what shipping is about, position, any navigational obstacles to look out for, how the boats travelling, sea state, wind conditions etc, reassuring to know all on board are on the same page.
If the weather builds and you think you need to change down do it early (some would says as soon as you think about it) rather then late.
Run minimal lighting on board except essential nav. lighting to preserve your night vision. We never used to read or watch movies as it trashes your night vision but did listen to ipod music and talking books pausing to do a 360 sweep every few minutes (it pays to listen as well as to look, you may hear something not quite right with the boat or in some cases hear another boat or obstruction before you are able to see it, one sailor I know heard the ship that almost ran him down in heavy rain before he was able to see it or detect it on radar!).
Be aware of shipping conditions, obviously in a heavy traffic area you need to be more vigilant.
Stow the boat so it's as quiet as possible for sleeping.
Set up a good sea berth, we used to pack extra cushions into the lee sheet berth or even put a cabin mattress onto the drop down in the saloon if that was most comfortable.
If your on watch and you find your drifting off stand up, dance a little, what ever it takes, there's nothing worse then being below off watch and hearing your crew mate snore!! Setting alarms is fine if your one up, two up and it just wakes the person trying to get some sleep and adds to their fatigue.
Enjoy, it's beautiful out there after dark away from it all.
I'm surprised that no one has mentioned the most obvious point yet ......... Do it at Night
1. Correct Navigation lights displayed at all times, whether sailing or motoring or both. If you are motoring with or without sails the masthead steaming light must be displayed. (Not your anchor light.)
2. A good lookout must be kept at all times. This means the watch on deck must be rested, aware and competent.
3. Ensure your compass has a light that makes it readable and TRUST your compass.
4. Plot your course and positions on a proper chart using observations and whatever navigation aids are available.
5. Maintain a radio watch on VHF channel 16 and where possible log in and out with coastal radio stations while in their area of coverage.
The above are your basic legal obligations, no matter the length of the voyage.
Your moral obligation is to have fun doing it.
