Hey, I go KCL. Both uni and london are amazing, but I've lived in London all my life so idk if i can give particular advice. All i can say try and find accomodation near a tube station (it will make life slightly easier)
There is so much to do here. The best thing to do is put yourself out there and make friends.
To make friends just attended all the welcome events and talk to people. Everyone there is in the same boat as you and also want to make friends. The more you show up to places the more people will recognise you and the more people that will come up and talk to you.