Shooting in low light and at night can be very difficult. While not everyone would choose to take pictures in low lighting or at night. There are many times when it becomes necessary or desirable to do so. Times like indoor parties, fireworks, and backyard barbeques that last into the night.
For low light situations, IE inside, Without blowing out your image. This is easier then you think. I turn my camera to manual mode. I set my apature to be F/11. I then turn my shutter speed to 1/50 and turn my flash on. However i turn the flash down to about -1 sometimes -1.5. Then it allows for some processing of the ambient light in the room and the flash will fill in your subject. Makes for a great inside picture.
If you are going to be shooting at night, turning your ISO up to a faster speed will help your pictures produce faster. Simply turning the ISO up will mean you generally wont need a flash while indoors in poor lighting. However your image will have a higher noise factor and will also have a color cast to it due to the lighting. Using your flash will help balance out the color cast.
Shooting night landscapes and cityscapes is easier then you might think. You will need a tripod and a auto timer or cable shutter. Set your tripod up and frame your image. Using manual focus, focus in your image. Using Auto focus generally can be difficult as the camera has a hard time seeing the scenery in the dark. It might focus on a cityscape easier though. I like to use Apature Mode when shooting night landscapes. I set my desired Apature for what i want to shoot. Generally a middle apature like f/11 or f/9 and let the camera set the speed. However if you want to decide how light or dark your image is, set your shutter speed in manual mode.
Remeber that taking photographs at night can be hard to do. You will always need a self timer or shutter relise. Otherwise just the shake of you pushing your shutter will cause blur in your photographs. and as always practice! There are many beautiful night and low light shots to be had! Go out there are give it a shot.