I believe that perhaps the most significant challenge for many photographers is image noise. I often struggle with this myself when shooting fast-moving wildlife.
For landscapes and flash photography, noise isn't usually an issue for me. However, when trying to shoot at faster shutter speeds, image noise is my main concern. Modern cameras have made significant improvements in image quality in the past few years. I certainly noticed a difference when upgrading from the Canon 5D Mark III to the Canon 5D Mark IV.
In this video, Duade Paton reveals four factors that cause image noise and how you can reduce the amount of noise in your photos. In his first point, Duade touches on something that I knew about but haven't attempted to try, and that is that a dark background will have more noise than a lighter one. I've always been picky about my backgrounds, but I've never really tried to get a lighter or darker one when photographing wildlife. This is certainly something I'm going to experiment with.
This video also covers ISO/exposure, camera types, and post-processing cropping as things that affect noise. As an added bonus, he ends the video with a short explanation of how he deals with high noise images during post-processing. Even if you're a seasoned photographer, a refresher is always a good thing.