I use a Nikon D90, and I want to take photos of gorgeous city lights at night! What settings do I use?

Put camera on a tripod then set camera to manual mode, ISO to lowest (100 or 200), EV to 0, smallest f/number and a shutter speed of 10 seconds. Shoot. If overexposed, make aperture a bit smaller (larger f/number). If underexposed, increase shutter time a bit. Yes, use self timer. Remember to adjust bit by bit until you get the desired results. To get longer light streaks from cars, increase shutter time but you have to decrease aperture size at the same time to compensate.