What should one do in London?

[Megas Methuselah]

Drink heavily. That's what the locals do. When in Rome, etc.

Going by that rule, you should also not brush your teeth or mouthwash in any way.

[Beefy187]

Watch some soccer match.... Though its off season now.

[The New Che Guevara]

I come from outside of London, yet have family living in the GLA.

Basically, go to the London Dungeons (Once is enough), Take the tube, carry a bag, dont take a tour bus... the guides are annoying. Take pictures, speak your own language, annoy the locals. Go see a show, just to say you have, invade the tower, and always... Go Staines via Waterloo. Catch the shuttle to Thorpe Park! Never a bad time.