A lot of this is repeat, but...
I do a lot of caching at night, and the best advice is to just use common sense.
I prefer to cache at night because of less muggle traffic, and also just due to practicality, as I'm busy during the day. I stick to caches that aren't really rural...but not exactly urban either. If I get a chance, I'll go out in the day and scope the area out for a few minutes, and come up with a game plan as to where I need to park, and where I think it may be. Then, I can go back after dark and take as much time as I need to look for it.
I do go by myself, which actually is kind of not a wise thing to do. Because I do go alone, I don't go too far from my car, I don't go to cemeteries or parks that are closed at night (a given), and I always keep my cell phone in my hand. I also always tell someone where I'm going, and approximately when I'll be back. If I feel uncomfortable, or see someone approaching me, I'll usually head back to my car. And...I'll also stay away from "suspicious areas" hehe...I'm not going to poke around government buildings, bridges, and the like too late at night.
As far as special equipment, I have a pen that I bought at Walmart. Its a working ink pen, but it also has a super bright LED light AND red laser pointer on the end. That way I have less to carry.