I avoid software that I know to be problematic. Also, I firewall off all outgoing network traffic by default, and whitelist very sparingly.

For my smartphone, I run a bare minimum of apps and refuse to install new ones without an extremely good reason. I also pipe all smartphone data through a VPN I run at home, specifically so that I can run it through my firewall and make the block-by-default policy I mentioned above cover the phone as well.

Don't do anything secret on the computer

Assume every system on Earth is breached