Hayden's point on changing defaults is spot on, but I learned the hard way with my own setup. Beyond that, put your smart gadgets on a guest Wi-Fi network so if one gets hacked, it can't reach your main computers. Also, disable any features you don't really use, like remote access on indoor cameras. Regular checks for software updates are key, since auto-updates sometimes fail. It took me a weekend to lock things down, but now I sleep better.

Yeah, it's always the little things causing the big problems.