London, Grosvenor Square recommendations?

Dammit man, get yourself down to a traditional boozer and immerse yourself in Real Ale. It's not flat and flavourless like you may have been led to think, and you'll get a taste for it in no time. For hoppy craft stuff that will taste exactly like what you drink in Florida just take some bottles back with you. Kernel and Beavertown are good. Job done.

 

Grosvenor Square is literally my work address, so I know the area well. Sadly, there are not any good pubs (talking about beer quality, not just atmosphere) within an easy walk. Apparently the well-heeled folks who can afford to live here (not many Brits anymore to be honest) don't appreciate that sort of thing. Therefore, I've got to give you the same advice I give for London in general...which is to refer to the following link:
https://www.beeradvocate.com/community/threads/london-beer-recommendations-for-visitors.96473/
Only caveat is that the Kernel doesn't do a tap room any more (only bottles for takeaway).
My top two places that I occasionally pop off to at lunch are the Cask Pub & Kitchen and the Craft Beer Co. Covent Garden. Near Covent Garden/Trafalgar Square (which I assume you may at least pop by to see) is also the Harp.
I also second @Hoppsbabo and recommend diving into cask ale while you have the chance here. All the places I mentioned will have a great cask selection.
If you have any specific questions about a place, just let me know. I've likely checked it out if it is within walking distance of Grosvenor Square.

 

Euston Tap is perhaps worth a visit if you have time. Quite a quirky old place with a decent, well kept selection.

 

There's a London thread still on page 1 of this forum - read that for recommendations. Public transport in central London is very good (you can spot Londoners in New York because they're the ones moaning about having to wait five minutes for a subway train) particularly if you get the Transport for London app and an Oyster card, so there's no point worrying too much about specific neighbourhoods.