So you wanna go to London? Good choice. I recommend it. There's a lot to do here and I've tried to gather my personal favorites into a cohesive post. Okay, maybe it s just a big lumpy jumble, but you can deal. Let's start at the beginning, shall we? (Remember that the hyperlinks are in bold. I think it's kind of hard to tell on this site sometimes.) AKA, all the boring stuff you don't want to plan, but it's your adult responsibility to do so. Sorry.
PREPARE YO SELF.
Seriously, check yourself before you wreck yourself. I think in the excitement of visiting a different country, sometimes people forget the practical stuff. The basics of getting around and navigating a new place should be high on your prep list, because it's probably different than you're used to. Unless you live in NYC w/o a car and then you're pretty much a pro. Everybody else, here's what you need to know:
0.) If I have to tell you to get a Passport, you should just stop reading and do that. And then you should maybe smack yourself.
1). Getting around the city. I would strongly suggest that you go ahead and buy yourself an Oyster card before you get here. (No, I have no idea why it's called an Oyster card. It just is.) Even if you're staying somewhere centrally located, you're going to need to use the tube at some point. It's easy to use, and you can avoid the lines and all of the confusion of buying single tickets, plus the card allows you to add money when you need it, which we call "topping up." (There are also some discounts for some tourist attractions if you buy it online, probably not the ones you want, but still.) In addition to the Oyster card, I would also make sure you have the Citymapper app. It's excellent - gives you all sorts of different route options and fare estimates, distance, and travel time. It also includes a feature to hail a taxi if you wimp out, I mean, want that. It has an offline map of the underground if you ever need it and can't get a signal, and nobody gets a signal when they're actually underground on the tube. You should probably get familiar with how it works before you get here.
Let's talk real quick about maps. Once you are walking around the city, Transport for London also has these navy and yellow signposts with the Legible London maps posted. They're very handy, and they give you an idea of what's within 5 or 15 minutes walking distance. They're pretty much everywhere in the city, but I often see people looking at their phones when a giant map is right at the end of the street. I've honestly had someone ask for directions while standing within spitting distance of a map and just pointed the way for them. (I hope I didn't make them feel as dumb as they looked at that moment.) You also might want to grab a tube map. You can usually find them at the stations and you can print them off from the TFL website. There's also a step free map and a map of toilets, which is more important than you're thinking right now. (Pro tip: the closest public toilet is probably going to be a McDonald's. A lot of places won't have toilet facilities for the general public, so if you're traveling with kids, look for the big M, or one of the ubiquitous cafes - Starbucks and Pret A Manger are other safe bets.) Another option for getting around when you're really lost is using an Uber car. They're cheaper than black cabs and you can call one to your location from the app on your phone, which also automatically makes the payment for you. (So set that account up ahead of time.) That said, I do think it's part of the London experience to ride in a black cab as well as the double-decker bus. You just can't come here and not do it. The cabbies know a lot about London, so go ahead and ask.
A word about distance in London. This won't seem like it makes sense, but London miles are different. It just takes longer to get through the concrete jungle. When you look at your map and think, "my hotel is only 6 miles from the Tower of London, no problem" you are not fully understanding that 6 miles is probably going to take you 30 minutes by car, 45-50 mins by public transport, or you could walk it in 134 minutes and burn 512 calories. My house is about 8 miles from the Tower of London and it takes me an hour to get there in the middle of the day, and at the least 2 different forms of transportation. I know I sound like a jerk, but really, I get a bit tired of explaining this to visitors that are just looking at a map thinking they can get anywhere in 15 minutes.
2.) Smartphones. You need to figure out if you're going to use your smartphone while you're here. That's gonna depend on you, your coverage, your carrier, your data plan. The key here is YOU :) I'm not gonna make that decision for you, mostly because I can't live without my phone, so you know where my sympathies lie. And also because much more has already been written in detail about it. A lot of people buy a cheap, pay-as-you-go, SIM card while they're here. You can get them at the airport and tons of convenience stores around the city have them. I'd recommend 02 if your have a choice.
3.) Money. London is expensive (esp if you are coming from the States). Everything is way more than you want to pay, so just get over it and forge ahead. I would exchange money at the airport when you arrive - not a lot, because they do take credit cards, but there are a few times you'll need cash. (Some of the public restrooms require 50 pence to use, specifically any of the the loos in public transport stations will require some change.) Which brings us to credit cards. The UK uses chip and pin cards, which are so much easier, so if you could get one of those from your bank that would be super helpful. Regardless, you need to check with your bank (or credit company) about foreign transaction fees - some charge a fee for each individual transaction, others just give you a daily rate. The only thing I would NOT do is get a cash card from Travelex. They try to push these, because they work like debit cards. In theory a good idea, but Travelex sucks. Seriously. I kind of hate them. My dad just had a horrible experience with them, that required returning to Heathrow to prove that he had given them hundreds of dollars. You don't even want to hear this story. Cal and I also had a somewhat lame experience with them when we moved.
4.) Where to stay. As for where to stay in the city, that's kind of tough and depends entirely on what you can afford. Decent hotel rooms average about $200 a night, and that depends on the season. If you want to be centrally located and you don't want to be in a dodgy neighborhood, you'll probably have to pay through the nose. Insert smiley face. (Nice neighborhoods in London are posh and flush with money, so the rest of us have to live elsewhere:) I recommend Airbnb - you can find something reasonable and something less expensive than a hotel. I know some people find it weird, but trust me, it's not that weird and I've had good experiences every time I've done it. Check the reviews on airbnb for places that look interesting, I've always found them to be helpful and accurate. That said, if you do want a hotel room - there are loads to choose from. There are lots of the chains you're familiar with - Marriott, Hilton, Radisson, etc. (Marriott owns The St Pancras Renaissance and it is incredibly grand and right by Kings Cross Station.) There are plenty of trendy boutique hotels - there's an Ace Hotel in Shoreditch, The Hoxton in Holborn. (You might have to flash a hipster card or at least pack all of your skinny jeans and beanies. But seriously, they're cool and I think I might go stay a night in one just for fun sometime.) To figure out what area you want to stay in, figure out what you want to do while you're here, pull out the tube map and find an area near your choices. East London is for all the cool kids. North London is for the real Londoners, West London is for the affluent families, and South London is what they call, "up and coming." J.K. Rowling lives in Kensington, if you want to try to run into her. Not everything happens in Notting Hill though, despite my attempts to run into Hugh Grant. It is very charming, very trendy, and not as central as you think, but it's definitely only a few tube stops into central London. London has lots of parks and green space, so finding a place near a park will provide you lots of opportunity for evening strolls. And if you're not near a park, you should go to at least one of the Royal parks while you're here. I insist.
5.) What to bring. Good walking shoes. Learn to love walking, and then learn it again. You are going to walk. A lot. You'll also want a light jacket that blocks wind, and a compact umbrella. (Unless it's winter and then you're gonna need your cold weather gear.) Bring your camera, duh. Back up batteries for that camera and probably your phone while you're at it. Comfortable bag for schlepping all day in the city. Bring an adapter for your electronics (make sure to check their voltage as well). Bring your good times and your laughter too.
Leave your bad British accent at home. Nobody wants to hear it.
I think this is a good place to take a breather. Don't worry, I know this isn't the stuff you want to know. Sights and eats are next post.