General

Turn off lights when you're not in the room
Take regular readings of your meters and make sure they tally up with what you are being charged.

Check with www.uswitch.com that you are with the cheapest provider for your area and useage.
Don't leave things on standby.
Understand how you are charged – if you are on ecomony 7, consider getting some timers so that you can set your appliances to start whenever your cheap hours are.
More information from the Energy Saving Trust.