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Home WiFi security gets either ignored completely or turned into a weekend project. It's neither. There are four things worth checking, they take about five minutes between them, and after that you can reasonably stop thinking about it.
This is by far the most important one, because it determines whether someone sitting outside can read what you're doing. Your network will report one of these:
If you're on any of the bottom three, go into your router's wireless settings and switch to WPA2, or WPA2/WPA3 if offered. Pick a long password - length matters far more than special characters. Three or four unrelated words is both stronger and easier to type on a TV remote than a short jumble of symbols.
WPS is the feature that lets you join a network by pressing a button on the router or typing an eight-digit PIN. The button is fine. The PIN is the problem: a design flaw means it can be brute-forced in hours, and that hands over your actual WiFi password. Once someone has it, changing the password is the only way to get them out.
Unless you rely on it for a device that has no other way to connect, switch WPS off in your router's wireless settings. Nothing else about your network changes.
Protected Management Frames (also listed as PMF or 802.11w) stops an attacker from forging the messages that disconnect devices from a network. Without it, someone nearby can knock your devices offline repeatedly - irritating on its own, and the first step in tricking a device into joining a fake network instead.
It's mandatory under WPA3 and optional under WPA2, so a WPA2 network often has it switched off even though the router supports it. If you find the setting, enable it. Very old devices occasionally struggle, in which case "optional" or "capable" mode is a safe middle ground.
This is separate from your WiFi password, and it's the one people forget. It's the password for the router's own settings page, and on many routers it's still admin / password. Anyone already on your WiFi - a guest, a neighbour who got the password once, a compromised smart device - can otherwise reconfigure your entire network. Change it, and while you're in there, check for a firmware update.
Hiding your network name. It feels like stealth and isn't. A hidden network is easy to spot with standard tools, because it still transmits and your own devices constantly shout its name looking for it - which arguably leaks more than broadcasting normally does. Meanwhile connections get slower and some devices fail to reconnect reliably. There's no security benefit to trade for that.
MAC address filtering. The idea is to allow only known devices, but device addresses are sent unencrypted with every packet and can be copied in seconds. It stops nobody who is actually trying, and guarantees an annoying afternoon every time a visitor needs the WiFi.
Cheap smart plugs, bulbs and cameras are the least well maintained things on most home networks. If your router supports a guest network, put them on it: they still reach the internet, but they can't see your laptop or your files if one of them is compromised. Many routers also let you disable guest-to-guest communication, which is worth switching on.
Related: Slow DNS and encrypted lookups · Weak signal and dead spots