Apple's Touch ID is great -- when it works. If you're having some trouble with your iPhone recognising your fingerprints, it's time to train it a little more.
We already covered how to do the initial iPhone training by trying multiple angles or even registering your finger more than once. Instead of deleting the finger from Touch ID and trying again, iOS lets you add to your fingerprint.
Open Touch ID & Passcode from the Settings app. Then just press your finger on the home screen and you'll see the fingerprint icon highlight. You just sent your Touch ID back to school without starting over. Touch ID has more information about that finger. Try this tip if your iPhone never seems to record your fingerprint correctly.