Reduce and avoid noise in photographs. Try using a lower ISO setting if you take pictures in low light conditions. If you're shooting with extended exposure, consider using a noise-reduction filter. Make sure you have a stable tripod.
Try using a remote trigger. To avoid digital noise in photographs, the first step, and the most basic, is to take photos in RAW format. In my case, I always shoot in RAW, so this option is disabled on my camera. The best way to reduce noise in an image is always to avoid it in the first place.
Methods such as adding artificial light, increasing shutter speed or expanding apertures so that more light enters through the lens are effective ways to illuminate the exposure rather than increasing the ISO. However, if this isn't possible, your noise reduction toolbox should include one of the methods mentioned here. Some cameras have built-in noise reduction, which could be useful, but it's not a feature I use, since noise reduction is very simple in post-processing. In the Lightroom development module, you can reduce the appearance of noise in images by using the luminance slider in the details panel.
Simply move the slider to the right to reduce noise, being careful not to push it too far. Excessive noise reduction can cause a loss of detail in the image, giving them a “plastic” appearance, so be sure to keep an eye on the overall appearance of the image when using this feature.