If your gas or electricity is already provided by us, you don't need to do anything. As we doesn't support prepayment meters, you'll be contacted to arrange for a credit meter to be installed instead. This will be much more convenient for you and will mean that you will no longer need to top your meter.
If you're on supply with another supplier, it's important that you contact them and let them know that you've moved into the property and that you plan on transferring away. This will prevent you paying the incorrect rates, or someone else's debt.