One camera feature that is sometimes overlooked by photographers is Auto ISO! This is a mode where the ISO setting is adjusted by your camera to a setting that the camera predicts as a useful choice without you having to manually adjust the ISO all the time.
This is an especially perfect option when shooting handheld. When your camera is in Aperture Priority Exposure Mode, the camera is “thinking” about what ISO would be right to ensure the shutter speed is fast enough for handheld photography, minimizing the effect of motion blur caused by hand movement. It also takes into account the focal length you are using, and it does a great job at making a good choice for the ISO value to be used. It raises it automatically in lower light scenarios, but then brings it back down to lower values in brighter circumstances. That is exactly what you would want it to do!
One small distinction is with regard to Nikon cameras: Nikons have something called ISO Auto Sensitivity Mode. Rather than totally surrendering control of the ISO to the camera, as other brands do, Nikons allow you to still set the ISO value, and then when you enable ISO Auto Sensitivity Mode (in your menus), it will automatically will override your ISO choice if it thinks your choice is too low for handheld photography when in Aperture Priority Mode. That’s still a great feature! You could just set your camera to ISO 100 or 200 and just let the camera raise it automatically as needed.
Also, Auto ISO is quite useful in Manual Exposure Mode! In this mode, you then take control of both the aperture AND shutter speed, and the camera will try to choose the right ISO value that will work for that aperture/shutter combination (at least within the limits of your camera’s capabilities).
SO if you have never used Auto ISO before, I encourage you to check your user manual and try it out!