Here are two tactics for after-dark traffic stops that I have found useful:
When using your spotlight on the driver's side mirror, approach from outside the path of the spotlight beam. I hold my flashlight in my non-gun hand, pointed behind me so oncoming traffic can see it (just in case those overheads and arrowstick aren't obvious enough!). Then I make sure I take a wide enough path to the driver's window so I'm not silhouetted in the mirror by the spotlight. I've found that if I keep an eye on my shadow on the ground in front of me, and make sure it never touches the car, the driver cannot see me coming. I've had drivers jump a foot when I reach their window because they're so startled I'm there. Of course, I wouldn't try this where traffic is so heavy that the wide path to the stopped car would put me at too much risk, but that path isn't as wide as you might think.
When doing a passenger-side approach, walk behind your squad—never in front of it—to get there. Walking in front of your squad will silhouette you with the spotlight, take-downs, and headlights, and the occupants of the stopped car will know where you are. Try these with a fellow officer in a parking lot some night like I did. I was instantly sold on both tactics, and I use them on every stop.