Cont will give you continuous ignition on the selected igniter(L OR R), FLT will give you ignition on BOTH automatically. 1st flight of the day use the right igniter to start engines. Why? Cos its powered by the AC standby bus, and therefore could be the only chance you have to start an engine at altitude in the event of a double engine flameout. ie if the right igniter wont work, you aint got no spark plugs if the ac power fails.
If this happens at 37000 feet, its a long way down before you can start the APU and get power back on the busses