hey! well i'm not sure if you did a search or anything about this topic- but i did some posts while i was in London this past spring. Pretty much what other people said is great advice and very true. I only skimmed the thread (b/c i gotta run to Kansas City) but you are going to have an amazing time.
I was very homesick when i first got there for about the first month and had a hard time adjusting. However, once i was there, I LOVED it. I miss it a lot and can not wait to go back. I went with two of my best friends (not in my sorority though) which was a great decision but we met so many people, as long as you make an effort, you won't be lonely (not sure if your going with someone you know or not) and you'll meet tons of people through school though. Make an effort to see the country and to travel though- i had to work while i was in london (b/c it was so expensive there!

) so i didn't have an opportunity to see the rest of england but i did get to go to France, Italy and Ireland (dublin is freaking awesome!!!) So, travel and see as much as you can
you're going to find out how much you are capable of and you're going to learn quite a bit about yourself. I had a whole new view on myself and my life when i came back, that is something you really can't put a price on since you'll have those experiences for the rest of your life.
In regards to greek life, as others have said... E-MAIL EMAIL EMAIL! lol AOL instant messenger is great to keep in touch (mind the time difference though) there are tons of internet cafes and plus you'll have internet at school- I sent tons of postcards and kept up with everyone that way- i would call on sunday nights during meetings and talk to everyone (you can get good phone cards too) it would make me miss everyone- but its nice at the same time too.
My advice is to not get so attached to missing home- like- don't call home and your friends/ boyfriend EVERY night- go out and get lost in the city during the day- make plans for night- if your concentrating on missing everyone- then thats what your energy will go into- thats the mistake i made.... do you know what i mean?
anyway- have an AWESOME AWESOME time- keep us updated- and i wish you the best
~maggie