The Chaotic Joker and His Plan
Joker states that chaos needs no plan, yet we see that in every action he does, there is a hidden scheme going.
When Joker kidnaps Rachel and Harvey Dent, there are actually two schemes that are having effect. First, upon the kidnapping, he intentionally has himself arrested so that he can taunt Batman and force a cop to activate a bomb using phone call. This scheme will only be obvious near the end of the film.
Second, when he tells Batman to choose between Harvey and Rachel, he actually plans that Rachel will be killed because Batman will decide to save Harvey. Another scheme that is going is that Joker has planned that Harvey will be saved because he wants Harvey to become Two-Face from the very beginning of the plot.