You would need to ...
1. Make sure you don't leave the device where someone can access it.
2. Make sure you are careful about what sites you visit on the phone.
3. Be very careful about the apps you install, even from Google Play. Also, of what items you get and/or install through an app.
4. Don't use public WiFi connections or only access them when you choose too, rather than have it set to do it automatically.
5. Update the phone and apps to watch and restrict the WiFi access.
6. Just turn off WiFi when not planning on using it. Yes I know some people think they can't do without it, but having it on 24/7 is a risk. Especially if you are set to access any open WiFi you come in contact with.
7. The same goes for your Bluetooth. If you aren't using it at the time, turn it off.
8. Don't download things to your phone from any site or email if you aren't 'sure' it is safe to do so.
9. Install Antivirus on the phone, as well as monitoring software.
Those are the best options for keeping your device safe.