Lens doesn't matter much. Exposures will likely be long, on the order of a second or so, even with a fast lens, so use whatever you have. A zoom can be handy if you want to do abstract stuff (see below)

I would suggest you set the camera to Manual exposure. Otherwise the camera will try to make all your images look like daytime. Start with aperture at f/4 and shutter speed between 1-3 seconds. You can up the ISO to 400 or 800 if you want a faster shutter speed. You'll have to review the shots on the LCD and adjust as needed.

Manual focus is probably a good idea as well, as autofocus is unlikely to work well in dark conditions.

You can get some amazing abstract shots of street and car lights with long hand-held exposures. Experiment with panning or zooming during the exposure. Results will be hit and miss, but you will sometimes get really amazing effects.

You can also intentionally take out of focus shots and get some nice abstract bokeh shots.

If you have a tripod you can have images with buildings nice and sharp, but have a lot of ghost-like motion blur with people, cars, or amusement park rides.