The red live should be permanently live. The black wire with the red sleeve is what is known as switched live. it goes to the lamp; when the switch is off it should not be live, but when the switch is on it connects to the permanently live red wire so that the lamp lights. It matters little which wire is connected to which but personally I'd connect the black to common. Mainly because if you have a double throw switch, then when off the live is just on the one connection, which seems safer to me somehow.