While I've no objection whatsoever to the idea of turning off lights that aren't needed, I will point out that it doesn't actually save a great deal of money:
Using LED bulbs, a bedroom might be lit by 10W and a living room by 18W. Leaving those on continuously would only cost around 5p and 9p per day, respectively. It's heating things that costs the most money, whether that be heating a room, heating the water in a washing machine, heating the air in a tumble dryer or heating the water in a kettle.
I already use minimal electricity for heating anyway. The only heater that's normally in use in my home is a single oil-filled electric radiator, which I try to use only on its lowest setting. I aim to keep my 'warm corner' (next to my desk) at around 16C, although I see from my thermometer that I can turn the thermostat down a bit right now, as the temperature is currently showing as around 17.5C. (I might just be a little bit naughty though, and leave it where it is. The cat on my knee seems to like it!)