You don't. Android has pretty good "defense in depth" security, from screening in the Play Store, to the app sandbox, to kernel hardening. If you only get repu

You don't. Android has pretty good "defense in depth" security, from screening in the Play Store, to the app sandbox, to kernel hardening. If you only get reputable apps from reputable sources, have an eye on phishing attempts, and have no reason to think you are a target, you may afford to have a few weak spots in your system. A lot of people run outdated Android version, and most don't get hacked, and among those who do, it is almost always phishing techniques that software updates wouldn't have prevented. If you really can't, it you have a popular, higher-end Android phone from years ago, you may find up-to-date custom ROMs, that you can further optimize for security.