I thought this interactive animation explaining how WiFi works was pretty instructive.
Dave Hamilton wrote up some great Wi-Fi tips from a recent interview he did with former Apple Wi-Fi engineer Alf Watt on his most excellent Mac Geek Gab podcast. The first tip, using the same SSID name for multiple radios on your network, was new to me. I’d always thought you should give each radio a different name. I’ll be fixing that tonight.