Definately use a tripod. I was shooting 400 ISO film for some night shots here in Savannah, GA and as already mentioned definately bracket.
With night photography even exposure changes of 10 seconds to 30 seconds can show little to no change in exposure.
You will also want to take a look at the data sheet for your film that you use and check out its reciprocity failure compensation times.
It'll give you a good indication as to how many extra seconds to add on to your film, etc.