Writing a business letter
The Visual Communication Guy shows us what a formal American business letter can look like. I find it very clear to understand.
I don’t use a colon after the greeting. I learnt to use a comma, but now sometimes just leave it out! I would never end a letter with ‘Sincerely’. I would use ‘Yours sincerely’. However, I very rarely write letters now. Most of my correspondence is via email. I presume yours is to.

The differences continue …
Here are more words with different meanings in American and British English:
British American
film movie
ground floor first floor
holiday vacation
lift elevator
lorry truck
Can you see how this can cause confusion? For a British person, the ‘Erdgeschoss’ is the ‘ground floor’. For an American, it’s the ‘first floor’. So sometimes, before anything dramatic happens, you might need to double check to make sure you’re both speaking about the same thing! 😉
Football versus soccer
The popular sport of kicking a round ball into a large net (called the ‘goal’) is called ‘football’ in Britain and ‘soccer’ in America. What the Americans call ‘football’ is played with an oval-shaped ball. British speakers call this ‘American football‘ (link to: wikipedia.org) which should not be confused with ‘rugby’.
If you’re interested, you’ll find a nice chart comparing American football and rugby here (link to: diffen.com).

And more differences …
Here are yet more words with different meanings in American and British English:
British American
maths math
motorway highway
pavement sidewalk
petrol gas, gasoline
postcode zip code