I go there for work once a year. Do all the normal touristy shit. The eye. Palace etc. Get a train pass and head outside of London and see the country. Go to Bournemouth. Love that city. Head to the Isle of wright. Go stay at a B&B in the new forest. Get a train ticket from London to paris for $100 and tour Paris.
Two important things. After a night of drinking stay far far away from a kebab truck. Your entire next day will be ruined if you don't lol.
Find chippys and eat often. UK has some delicious food contrary to popular belief. Amazing curries , fish and chips and meats. The beef taste very different.
Oh their is Blackpool up north ( I'll be there in May). Its like a dirty Las Vegas.
Do not limit yourself to just London. England is a beautiful country. Explore