Use Optical Zoom rather than Digital Zoom.
Cameras now usually have Optical and Digital zoom functionality. Now when we used to shoot film we were using Optical Zoom.
Optical Zoom uses the lens of the camera to bring the subject closer. Digital Zoom uses software to digitally enlarge a portion of the image.
So why is Optical Zoom better?
Well Digital Zoom really isn't zoom at all. It just enlarges the image. You are losing quality because of the enlargement process. So the quality is better when using Optical Zoom.
So how do I know what kind of zoom I am using?
Well your camera will use Optical Zoom first, then Digital zoom. Check you manual for ways that you can have your Digital zoom turned off or how to notify you when you have gone into Digital zoom mode.
You are better off using Optical Zoom and cropping your photo in post processing.