Having your own copy of a tube map is a great lifeline when plotting a route. Get the London Tube Map app so you've always got the information to hand. Compatible with the iPhone.
Oyster Cards are what the vast majority of locals use to travel around London. Simply top up any amount you want and then scan it whenever you get on a bus or the tube. It's easy and saves you over 50% on prices.
With a London Travelcard you can travel on the underground and buses around London as much as you like for a one-off fee. To save you time and hassle, order online and get the ticket delivered in advance.