Long-exposure noise reduction Turn long-exposure noise reduction off.
Focus Turn off autofocus. Focus on the brightest object in the sky, trying to reduce it to the smallest point that you can. Use live view and zoom in live view to make the stars as small and sharp as you can. You may have to turn up the ISO or open up the aperture to make the stars visible in live view. Before I got a mirrorless camera with a good EVF I found it essential to use a loupe to view the display (e.g., a Hoodman HoodLoupe®). As a final check, shoot a test exposure and check it by zooming in and viewing it with your loop. It is wise to check your focus occasionally if you are shooting multiple exposures to be sure you have not accidentally bumped the focus when moving about and recomposing. I have experimented with a Focus On Stars tool (https://focusonstars.com/). It does not work with all of my lenses, but for those that it works with it allows me to focus faster and more accurately. I carry it with me everywhere I go.
Exposure settings I typically expose for 10 seconds with a very wide lens (11mm on a full-frame sensor). A shorter exposure might be better but any shorter has too much noise. Lenses that have a narrower field of view require a shorter exposure. I use the largest aperture (lowest number) for which my lens is sharp—f/4. In the past I used ISO 3200 but with my latest camera, I use ISO 1600. This ISO might seem very low, and the images are initially very dark, but by intentionally shooting dark images I preserve more color in the bright stars--the dark areas can be brightened in post. Shooting at a higher ISO or for longer blows out the bright stars and there is no way to fix that in post.
Capturing Light Frames If your camera has a mirror, to minimize camera shake, set the camera to live view to lock the mirror up. To capture images quickly to minimize the movement of the stars over the course of the capture, set the camera to burst mode. Using a remote shutter release or intervalometer, hold the shutter button down long enough to capture at least 10 images. Typically I lock the button on my remote release, set a timer for 5 to 10 minutes on my phone and look around for other compositions. When the timer sounds, I close the shutter and move on to another composition. Total exposure time is probably more important than the frame count. If I were to shorten my exposure I would still shoot for 5 to 10 minutes. There would be more images to stack.
Capturing Dark Frames For version 1.8 and earlier of Starry Landscape Stacker I recommend against the use of dark frames. For version 1.9 and later, I recommend capturing 10 dark frames immediately before or after the light frames. Just put on the lens cap and take 10 exposures with settings identical to what you used for the light frames. If you have a camera with very low noise, you might be able to get away with as few as 5 dark frames, thus saving some time. If your camera is extremely noise you might need more than 10. It is best to capture dark frames as close in time as possible to the light frames, but I have done experiments with dark frames taken approximately 24 hours after the light frames and at about the same temperature. Dark frames taken 24 hours later resulted in an image that was better than with no dark frames, but not as good as dark frames taken immediately after the light frames. If your lens cap leaks light, you might have to cover your camera with a dark cloth.
Capturing Flat-Field Frames Flat-Field frames are usually prepared at home before or after collecting the other images. See Preparing Master Flat Frames.