Shutter Speed: Set the shutter speed for the maximum shutter speed you can use with your wide-angle lens choice to keep the stars as points of light. The checklist below has my recommendations on shutter speeds for various lens focal lengths to minimize most of the movement of the stars. Review your image on the LCD screen with a loupe and if you see oblong shapes or trails, use a faster shutter speed until you see circles instead of lines.
Aperture: This will vary depending on how much light is in the sky. For a dark night use a wide-open aperture to get as much light into the camera as possible. With strong moonlight, such as the week around the full moon, you can set your aperture to f/4 or higher and still get a good exposure.
Wider apertures such as f/1.4 allow for lower ISO settings and less noise but there is a trade-off. With wider apertures, you’ll see increased optical aberrations of the stars; and a general softness becomes more apparent, especially at the edges of the frame. This is less of an issue with Canon’s wide-angle L-Series lenses like the EF 35mm f/1.4L II USM and EF 16-35mm f/2.8L III USM. On other lenses, using f/2.0 or f/2.8 will help significantly.
ISO: It is important to set the ISO high enough to get a good exposure. You don't want to have to lighten the images in post-processing. This will dramatically increase the noise when you are using too low of an ISO. Conversely, darkening the image in post-processing will result in lower image quality if you had used too high of an ISO setting.
Use Manual shooting mode and set the exposure so that it is on the plus side by one or two stops over the standard exposure reading of the sky. For a very dark night without the moon, settings of f/1.4 at ISO 1600 to 3200 or f/2.8 at ISO 6400 will get you in the ballpark for a correct exposure.