People are friendlier than you think.
During my first month in London, it is fair to say that I felt very uncomfortable. The pure amount of people in this city is enough to stress you out - But bear with it because they are part of the amazing charm. However always be on your guard as well. London is a big city and therefore inherently not the safest place in the planer.
Learn to enjoy your own company.
London isn't the easiest place to find friends. I am lucky enough to study here, which places me in a group of people who are all keen to make friends. However London has a tendency to keep you busy, and most of the time you will find that you're by yourself. I say embrace it! Some of my best days have been spent alone tracking the width of the city.
Always have a podcast (or ten) downloaded just in case.
I can't even count the times I've been stuck in rush hour traffic without any form of cell phone connection. I've learnt to always have a couple of podcasts on hand to ease the experience. My top three right now are: My favourite murder, My dad wrote a Porno and Dressed: A history of fashion.