Security always a topic at this world.
Let begin from Wifi password, make a long length with combine letter, number and symbol.
Hide wifi SID rather than keep broadcast it over the air.
Change the default admin password.
Keep your eye on monitor router or telco app usage if any suspicious event, connection happen.
The rest depend on your router security function.
Example, DHCP only assign IP address to known MAC addresses.
Create separate VLAN for visitors or temp users. (My friend's neighbor ask one time password and use it forever)
And many more depend how much you know those technologies.
A lot of time, the event happen with people you know.
Example, my wife's phone update app or download firmware when connect my BB plan. My wife don't even know it happen.
Thanks for the brief idea. There are gadget in the market to hack and use the router. Is there a way hide the Mac address of router?
Hide the SID and allow only known Mac Address device are good practice.