Good Luck LondonLover! You're going to have a blast! If you're a history lover like me DO NOT miss the Tower of London. I know it's a major tourist destination and the lines for it can be pretty grim BUT it's well worth a visit.
Try not to stick just to the major tourist places because you'll end up holidaying with Australians and Kiwis and you can come here for that! I got myself a flat in one of the Northern Boroughs which was cheaper than the west where everyone else goes and even though the area itself wasn't exactly posh (or clean) I felt safe and I was happy and I loved the ethnic diversity of my area.
You end up developing a love for the grittiness of London. It's part of the charm