In almost every genre, you will encounter situations in which you are using your lens' widest aperture and you can't make your shutter speed any slower, meaning all you can do is raise your ISO. That will introduce noise into your images, but thankfully, modern post-processing software can do quite a lot to correct that, and this excellent video tutorial will show you how to leverage it to do just that.
Coming to you from Anthony Morganti, this great video tutorial will show you how to deal with high-ISO noise in post-processing. One common mistake I see many newer photographers make is using too slow a shutter speed for the action they are photographing (or for preventing camera shake) in an attempt to keep their ISO down for better image quality. While it is true that raising the ISO will introduce some noise, that is something you can always work on in post. On the other hand, if a photo is blurry due to too slow of a shutter speed, there is generally not much you can do to save it. So, don't be afraid to raise the ISO if it will help you get the shot! Check out the video above for the full rundown from Morganti.