ok, i think that i know how....i read about it in a book
the principle is that somke keeps the light generated by the bulb and so it doesn't all fall on the sensor
the idea is to build a tube the bulb in one end and the LDR in the other end. then make sone holes at the middle of the tube so that the somke can get in. the idea is to put the device in a place that doesnt have ambient light, because it will not work.
but even this way you still need more components for the detector circuit. like at least a variable resistor and a device to be as an alarm.
but you have to advust the circut so that it will trigger at the smallest amount of smoke, even though the circuit will not be very sensible.
the circuit i saw in the book was a bit more complicated. it used a LED and a modulated light for it so the circuit was imune to the other light as long as it wasnt too bright. i think it used a photo transisto and it worked with IR, not normal leds.
hope that at least i gave you and idea of what you want to do.