Can anyone help re economical use of gas heating?

I have Glowworm flexi hx gas boiler. All with thermostatic valves. I am unsure if I am using it efficiently. When they say on the tv ads to turn it down a degree do they mean the setting on the boiler or on the thermostat on the wall? Is it more economical to have all the rads in the house on (low in bedrooms) or just on in the rooms I use? Is it better to keep on all day or turn off at times during day.. At the minute my thermostat on the wall is set to 20 and the reading on the boiler set at 69. If I am adjusting do I keep the setting at 69 on boiler and vary the wall thermostat setting? Any help appreciated. Thanks.