Love me some night photography! Like some have said, some of it is experimentation. If you do use a tripod, inevitably, there will be something to screw up your shot when using long shutter speeds.
Something to bear in mind, too, is the effect of backlighting; especially in city scenes. You can sometimes use brighter lights behind the buildings in your FOV to highlight or accent certain background areas more. Also be aware of where hotspots will shot up.
Tripods are fun...
...but, I like night hand held shots better although it does require a bit of patience.
I find them more rewarding.
