This has really come about since doing some night caches and the issues that arise from doing them.
What precautions should you take before under-going a night cache?
There are a few, many of which are in common with simply hiking at night, but some are specific to geocaching.
Firstly, the old scouts saying of be prepared! Make sure your torches, whether hand held or head, are properly charged (or you have spare batteries for them) as you don't want to get caught out in the dark without a light source. This also goes for your GPS, spare batteries or keep it charged (and a good old fashioned map doesn't hurt either!).
Secondly, take good note of any warnings on the cache information page - for example the night caches near Coombe Hill in Buckinghamshire have a person limit on them due to the proximity of the location to Chequers (Prime Ministers's home) too many people can lead to men in suits with guns coming up and asking what you're doing (though the Chequers staff seem to check the event page now and then as they don't bother us for the Midnight events!).
Thirdly, consider your terrain, a LOT of night caches are trails... meaning you'll only get the start coordinates. Take care to waypoint the main caches or markers on route so that you can get yourself back to the start without incident... we took a 'short-cut' once and ended up scrambling up and down a 20ft gully in the middle of the forest, we really should have followed our waypoints back.
Fourthly, the weather... recently a friend of mine did a seriously cool sounding Zombie night cache... but due to the horrific rain, and getting lost, the cache lost a lot of it's appeal!
Fifthly? Take a compass! Seriously... heavy tree cover or proximity to a pylon has on more than one occasion skewed our GPS positioning, and when you need to find 'the north east track after 50 paces' you may struggle when the GPS leads you astray.
When night caching and looking for tack markers on trees, this can seriously seem weird when they blink at you (it was a deer in our case!) - you're not the only one out and about a night so simple common sense of respecting your surroundings is pretty important too.