1. Lock your homescreen
2. Use caller protection apps
3. Avoid Charging your phones in public ports
4. Stop jailbraiking or rooting your phones
5. Use Two Factor Authentication
6. Update your phone's software regularly
7. Turn off your Wifi and Bluetooth if not in use
8. Encrypt hotspots by being used by other device
9. Store passwords in encrypted files
10. Use VPN to stay anonymous
-snip-
Read here to further understand.
Number 2 is important but many one don't aware about this, especially when they don't find trusted app they need, they installed because they think need that app.
Read this https://www.gearbest.com/blog/how-to/how-to-protect-your-cell-phone-number-and-why-you-should-care-3519 some have not been mentioned in the OP.