Hello!
Even though the iPhone 7 is a great camera, you should also make sure that the lighting is good where you are taking the photo, as well as this make sure that you're focusing on your subject by tapping on it.
The following link has more information on how to take great quality photos:
Take and edit photos with your iPhone, iPad, and iPod touch - Apple Support
If your iPhone 7 camera still isnt as good as what you are looking for try the following link to help you:
Get help with the camera on your iPhone, iPad, or iPod touch - Apple Support
Hope this helps!