Tell people you're Canadian aye buddy.
Learn the tube map, buy and oyster card - buses don't take cash. Enjoy London Pride - it's a beer, not a gathering of LGBTQX.
A Pint is 20oz and a gallon has 8 pints unlike the puny American ones. We use the Celsius system like all bar one other country on earth. Avoid the M25 and drive on the left. We have many roundabouts, give way to traffic coming from the right. Stop at red lights, no turning!
After drinking all night, always eat a Kebab also known as a Doner to blend in. Never tip in a pub even for food. Seldom tip over 10% in a restaurant. Avoid the night bus unless you like the smell of sick and urine.
Wanker can be a term of endearment or an insult. Chips are fat fries, Crisps are chips. The ground floor of a building is the ground floor, not the first floor. We eat a lot of curry - Korma is mild and Vindaloo is very hot.
Scotland and Northern Ireland have their own money, you may see these now and again, they are legal tender.
Black stuff is Guinness.
Calling a black person coloured is a no-no. Colour has a 'U' in it. Organised has a 'S' etc.

Moved from London 15 years ago The trick in my day was to find a place just outside travelcard Zone 2 when the accommodation costs drop, but within walking distance of a zone 2 station where the travel costs and times drop. Acton and Tulse Hill were very affordable. If you were a bit more well heeled then Camden was where all the cool kids lived. A few years ago Hoxton and it's North East London surrounds used to the up and coming place for up and coming hipsters.

Have you picked a Football (Soccer) team yet?

Welcome. You are very brave.

Good luck with the visa.....can’t offer any help there though...sorry. I live in Northern Ireland which is too far away to be of any practical help to you if you’re looking for accommodation around the London area. All I know is it’s very expensive, unfortunately! Hope all goes well with your plans to come to the UK...you are coming at a very uncertain time in our history.