Every year the Touch ID sensor on iPhone and iPad gets a little faster and more accurate. But few people 
know that you can also train Touch ID to recognize your fingers better. Remember that initial setup process where you touched the ring until the fingerprint on your screen filled in? Well you can add even more fingerprint data to the secure enclave chip afterwards.
Go to Settings > Touch ID & Passcode. Enter the passcode you use to unlock your iPhone. Now just touch the Touch ID ring (don’t click). In the list of the registered fingers you’ll see the reognized fingerprint turn grey. If you release and touch, your iPhone will collect more info about your fingerprint every time it turns grey. When you pick up your iPhone you may not always pick it up squarely and deliberately, so make sure to get it from all of the other angles and different parts of your fingers that you might hit the ring with. Maybe put your phone down and pick it up several times to mimic quickly grabbing your phone. Keep going for a couple of minutes with each finger.
While you are here you can add more fingerprints, or you can rename or remove your fingerprints by tapping them.