Common faults on lighting circuits
First step is to have a torch and switch off all lights if safe to do so. Check to see if breaker (fuse) will reset. If it still doesn’t then likely to be a fault in the wiring. If it does reset then go around and switch on each light one at a time. If the first light comes on and doesn’t trip the breaker then continue switching on the rest. If the first one trips the breaker then switch it back of then reset the break. Leave that one off and switch on the others.
You need to look for the light, which trips the breaker to identify where the problem is. One you have located the fault area then if it is a filament lamp try replacing it and see if it now works. Most other causes require and qualified electrician to locate and remedy the fault. Most common faults regarding lighting circuits are:
Blown filament lamp causing a dead short inside the lamp.
Loose or disconnected cable in light fitting caused by poorly installed fittings. These faults can take years to manifest.
Ingress of water into the fittings, switches or connections. Very common after flooding or on outside lighting
Burnt cables caused by cables lying on top of halogen spotlights in ceiling space.
Burnt out ballast in fluorescent fittings or transformers for low voltage lights