My wife and I honeymooned in England. Stuff we learned:
1. There is no tipping in the pubs, and tax is built into the prices. So, if something says it costs 20 pounds, it means that is what it costs. We overestimated our food budget by about 15-20% trying to account for tips and taxes that weren't there.
(That said, there ARE restaurants where tipping does sometimes happen. So, when in doubt, ask.)
2. Travel by train when you're there, and book the tickets early. England has a world-class transit system, and my wife and I never felt the need for a car.
3. Spend most of your trip out of London. London is an amazing city, but it is also its own entity, and the rest of England is very different.
4. When you are in London, get an Oyster card - it's the easiest way to travel in the Underground and the public transit.
5. You cannot do the Tower of London in a couple of hours. It's not possible, do not try. Give it an entire afternoon, and enjoy the hell out of it. With luck, the random dragon made from weapons and shields is still in the White Tower.
6. Canterbury is a great place. One of our regrets is that we only day-tripped it. You can see everything in the city center there in a day, and the cathedral is amazing, but it's a REALLY pleasant place. I honestly wish that we had spent an extra day there to just enjoy the parks and the city walls (which are Medieval, and intact). And, there's a hotel that is literally on the cathedral grounds (one of these days, we're going back and staying there).
7. Nottingham, in particular the Trip to Jerusalem. It's a pub carved into the caves under Nottingham Castle that has been there since 1189. And the food is delicious (we went there twice). Nottingham itself, though, is mainly Robin Hood-based, so there isn't much touristy stuff to see. But the Trip to Jerusalem by itself is just worth it.
8. TK Maxx is a great place to buy clothing. I got a brand new lambskin leather jacket for under 70 pounds - good luck finding a price like that in Canada, at least. Come to think of it, clothing as a whole seemed cheaper in England - I nearly came home with a brand new suit, the prices were that good.
9. The Holy Island of Lindisfarne - if you have time, go there. Seriously. It is the site of the first Viking raid in history, but more to the point, it is the most peaceful place I have ever been in my LIFE. It's a tidal island, so when the tide comes in, you're alone with a few people in a small village and the sheep (who set the pace of the island). All of our future travel plans for England involve spending a week in Lindisfarne at the end, just to decompress. But, if you're going to go, reserve your accommodations TODAY. They are few and far between (it is not just a popular tourist site, but also an important pilgrimage site), and it may already be too late to get something. If can't get accommodations on Lindisfarne itself, though, the island is a twenty minute cab ride from Berwick-Upon-Tweed, which itself is a nice place (with an intact Elizabethan wall system, which does not look as you think it might - seriously, don't mistake it for hills, or you're going to find yourself on the receiving end of a 20-30' drop), and you should be able to day-trip it. Also, there's the Lindisfarne Meadery, which has some REALLY nice mead. I think we came home with four bottles, and we would have brought more if we had the space.
10. Money and currency: your credit cards should work, your bank cards are hit-and-miss. HOWEVER, we found that anytime we were able to locate an HSBC bank machine, we could not only pull money out of our account, but also got a good exchange rate out of it.
11. When you plan your trip, know what you want to look at. England is a place where you can't walk more than five paces without tripping over some history, and it is physically impossible to see everything. So, get an idea of what sort of things you want to see, and plan around that.
And, I think that covers it...
On a related note, if you type "Canterbury Cathedral" into Google maps and hit "Street view," it takes you inside the cathedral. That doesn't do justice to the place by a long shot, but it's a good way to get a taste of things to come...