This could be a serious problem.  If all the lights are flickering before the breaker pops, then something on that line is likely causing the problem.   Check what devices and plugs and lights are out when this breaker is tripped.   Do not rely on a legend in the door of the fuse box - as it may not list every thing that is on the circuit.    Check for lose light bulbs, sockets that rotate when you turn the bulb.   On outlets, are the wires plugged into the outlet warm or hot to the touch.  Is the outlet itself warm or hot to the touch?   If you find any of these conditions, either replace or repair the suspect item.  This could include a lose wire in the wall, or a bad outlet or lamp socket.   If in doubt, call and electrician.

Number one cause of home fires in electrical - play it safe.