Instead of repeating all the information about low energy light bulbs, cavity wall installation and A-rated appliances, I'd recommend that you have a look at these two websites which provide pretty much all the information you could ever need on energy saving and saving money on energy:

http://www.energysavingtrust.org.uk/

http://www.uswitch.com/

This might also be useful though:

http://www.guardian.co.uk/lifeandstyle/2010/jan/05/how-to-make-draught-excluder