3. Use an Oyster Card
The Oyster Card is a pay-as-you-go electronic smartcard which can be used to pay for all public transportation in London. If you plan to stay in London for a couple of days, then this is your cheapest option to travel in and around the city.
Fares vary depending on the type of transport you use, the zone(s) you travel in, the time and day you travel. Just load your Oyster Card and your good to go.
You can buy it before you leave and get it delivered to your home address so you’ll be ready as soon as you arrive in London.