I will list down steps to secure your macOS & iOS Wi-Fi Network.
Step 01: First things first, Update you Macintosh, iPhone, iPad, iPod touch & even AirPort Express, Airport Extreme base stations for latest software using Mac App Store.
Step 02: Choose Unique & Safe SSID (Service Set Identifier) Wi-Fi network name
Wi-Fi network name is case sensitive. Choose a unique name for your network and that isn’t shared by other nearby networks. If your SSID isn’t unique, Wi-Fi devices will have trouble identifying your network. This could cause network device to fail to automatically connect to your network, or to connect to other networks sharing the same SSID.
You can Edit your Wi-Fi Network name here: Open AirPort Utility from Utilities folder in Applications folder > Choose & Click on your router > Click on Edit > Click on Wireless Tab.
Step 03: Make your Wi-Fi Network Hidden
Hidden networks don’t broadcast their SSID over Wi-Fi. You have to manually enter Wi-Fi Network name to join that network. It will make harder for hacker to identify & enter your network.
To hide your Wi-Fi Network follow this steps: Open AirPort Utility from Utilities folder in Applications folder > Choose & Click on your router > Click on Edit > Click on Wireless Tab > Wireless Options… > Check Create hidden network.
Step 04: Password Authentication, Network Encryption & Security
The security setting controls the type of authentication and encryption used by your Wi-Fi router. Use WPA2 Personal security. WPA2 Personal (AES) is currently the strongest form of security offered by Wi-Fi products.
You can change security settings of your Wi-Fi Network here: Open AirPort Utility from Utilities folder in Applications folder > Choose & Click on your router > Click on Edit > Click on Wireless Tab > Wireless Security.
Hope this information helps,
Let me know in comments if you require more information.
Thanks & Regards
Mandar Apte