No. It's only a sequel to "Batman Begins" (which was the first in the current series of Batman films). It would help if you had seen that - you'd know who a lot of the characters are - but I would imagine that it's pretty easy to pick up.
You will most likely know Bruce Wayne, his butler Alfred, Commissioner Gordon and their arch villian The Joker from any number of previous versions of Batman, but there are enough clues in The Dark Knight to tell you who they are and what they do anyway.
If you are in London, go see the film at the Imax, some scenes have been shot with a massive screen in mind!