Taking great pictures of the night sky can be really challenging. Therefore you need the right equipment and your camera has to be set up correctly. So here is a brief overview on what you need to consider.
You should not use the the camera's “night scene”, “stars” or “fireworks” mode at all. These automatic settings just don't get the scenery right. Also don't use the automatic mode, where the camera will determine the aperture, shutter speed ISO. Often the shots will be underexposed. So set up the camera manually.
Usually the autofocus will struggle in low light, so the focus needs to be set up manually to infinity. As for the focal length, an 18 to 24 mm wide angle is fine to a start with. But if you want to capture pictures of entire (stellar) constellations or even single stars and planets, you will definitely need a proper telephoto lens.
If you are using a long focal length, you should use a lower shutter speed. In that case it is advisable to increase the ISO. But try to keep it as low as possible.
To avoid shaky images, a tripod is essential. Also the use of a remote shutter release can be really handy. If you don't have such a device or you can't connect it, just use your camera's self-timer. However, in the long run, using a remote shutter release makes the whole process a lot easier and more convenient.
Another issue at night time might be that the moisture in the air may fog your lens. Or even worse, causing small drops of dew directly on the front elements, which can produce horrible, blurry spots in the final picture. To avoid this you can simply wrap up the lens with a sock.
After you set up your camera, make sure to take some test shots. Don't be afraid and take as much as you like until you are satisfied with the results.