Understand:
Spend some time getting to understand your heating controls and make sure they're set-up best for you. The Energy Saving Trust have some advice on this here.
Heavy curtains and decorative draught excluders can make a nbig difference and of course putting on some extra layers, thick socks amd cosy slippers can all help as well!
Optimise:
To heat the room effectively radiators need good air flow around them, which means that they shouldn't be blocked by furniture or other clutter. You can also put reflective insulation behind the radiators to reduce heat lost into the walls. For tips like this large and small see the Energy Saving Trust again.
Switch:
Most energy providers offer "100% renewable" tariffs, but some providers are totally committed to renewable electricity and do much more to invest in renewables. These newer, smaller companies are often cheaper too, Octopus, Bulb and Good Energy are three such examples. Switching is now really easy, you can compare prices and make the switch happen here.
Transition:
Those tips are worth doing, but aren't going to change the fact that heating our homes generally still requires fossil fuels. We need to transition homes away from gas boilers and towards much lower carbon heating, like heat pumps. These work like fridges in reverse and use electricity to provide heat 2-3 times more efficiently than normal electric heaters. The Government's green homes grant makes now a very good time to invest in an installation if it works for your home. Find out more here.