Mashable's article 8 iPhone settings you should change if you like privacy, gives a nice privacy checklist for iPhone.

If you've had your iPhone for a long time, chances are you still have a 4 digit passcode. This is not necessarily bad, but you should definitely enable erase data after 10 attempts.

You should be aware, however, that enabling Touch ID is actually less secure if you are interrogated by the police. Your right to privacy is limited to why you "think" and say, your fingerprints are physical. This enables the police to force you to unlock your phone using your fingerprint legally.

I'm not encouraging illicit activities which need to be hidden, just making the little known fact available.