No one wants to overpay for the energy they use. One way to make sure you don't is to switch tariff regularly. If you've never switched you could save hundreds of pounds. Even if you have switched before, you should continue to do so toward the end of each contract period (usually 1-2 years) to make sure you're getting the best rate.
There are a number of switching websites out there, and many also have a freephone number (i.e. start with 0800) you can use to get in touch with them. Using a comparison website means you quickly find the tariffs most suited to you - listed by price. The following site have all been approved by Ofgem, so you know you're getting a good service - just remember to tick the 'show me all available tariffs' button to see the full range of deals from all energy companies:
Remember though, whilst switching tariffs is a good start, many households can save more money (and energy) through energy efficiency than they can through switching tariff. Check out our Take Action, Save Money section for loads of ideas.