Taking pictures at night require a high ISO and your images will most likely be quite grainy, which again often makes a good b/wh. I love taking pictures in the streets at night, using only the street lights or lights from cars driving by.
One trick you can use if you are not fond of grainy high ISO shots is:
FIRST use a tripod and shoot the scene, low ISO, empty, without any people. If it is difficult to find an empty moment, remember that a long shutter speed will enable people to walk by without being captured in the image.
It that is still not possible, several shots and merge these in PS, only keeping the empty areas. Make sure you have at leas one shot per empty area.
SECOND Turn your ISO up high, wide aperture (f/2.8 may be necessary) and then capture the shot with your character. In Photoshop you put this image as the top layer, and erase the scene around the person. The low-grain scene from the first shot will appear.
The only grainy area in the picture will be your person frozen in action.