Ah... overnights.
A few things come to mind in regards to safety:
1. It's a helluva lot easier to get to a scene before PD or FD does. That can be a good thing or a REALLY bad thing. Always think about what you are going into before you even start driving there. There are some stories you'll want to beat them to and others that you won't.
2. Make sure you are VISIBLE. Go to a uniform shop and get one of those reflective orange traffic vests. Alot of the time you will find yourself on the side of the freeway shooting an accident after 2AM when the drunks are headed home.
3. Check in with PD or FD when you get on a scene. That way they know who you are and why you are there. You don't want to pop up from behind a bush and startle a cop unless potentially getting tazed or shot is your idea of fun.
4. Don't be the last one to leave. If you see the cops taking off, pack up and get moving. You don't wanna be alone in some rough ghetto after the cops have just hauled away one of the local "homeboys". Especially if you're a white-boy like me.
5. Don't get all absorbed in your viewfinder. Shoot from your sticks, set up your shot and then while it rolls, look around and make sure you are still surrounded by more friendlies than unfriendlies. Remember, you are toting around several grand worth of ENG gear - to a crackhead looking to get high, that's like winning the lottery. All he's gotta do is kick your ass to get it. And you WILL attract such unwanted attention, trust me.
6. Drive EXTRA carefully. Many of the folks on the road in the middle of the night are not exactly law abiding citizens. Some are drunk, high or worse. I've had numerous close calls during my stringing tenure involving intoxicated drivers, and if I hadn't been as careful as I was, I probably wouldn't be typing this today....
7. Last but most importantly, if it feels bad, it IS bad. If you get that sick feeling in the pit of your stomach that says "I really shouldn't be here" then listen to it. I'd rather go tell the desk I'm a chicken than have the PD tell the desk (and my wife) that I'm dead.
I think that oughta get you started. I'm sure other seasoned overnighters will chime in as well.