Enjoy your experience!
There are are few better places to be, IMO, than London in the summer. It will be warm but not hot, mostly sunny and, best of all, light until after 10 PM. Crowds spill out of the pubs onto the streets and the whole city takes on a pleasant air. Contrast this to the winters when it rains and gets dark at 3.
Oh yeah, the Tube stations will be hot and sticky.