I like fingerprint readers on Android smartphones, but when you’re setting up this feature, you get the option to enroll more than one finger.
Well, I’m not suggesting that you might lose a finger or something (it’s possible, but quite rare these days), but even a small cut or band-aid can leave you having to type in your passcode. I tend to enroll four fingers (two on each hand — which fingers depends on the smartphone, where the fingerprint reader is, and how big the handset is) to give me the best unlocking flexibility.
Additionally, I tend to enroll the main finger that I use to unlock my phone twice. I find that this makes the reader more reliable and less likely to be thrown off by small scars or some dirt.
Doing all of this takes a few minutes, but it will save you a fair bit of frustration down the line.