There's an early background tell on how Joker works.
During the heist he pretends to be just one of the faceless goons to prevent them getting wise that he'll picks them off after they're no longer of use.
He does something similar with the crime lords.
Once he's in with them he pretends to just be Chechen's new Scarecrow, occupying Batman and the cops for the kick, which isn't entirely wrong.
I'm going to detour for a second to admire the use of the three crimelords in the plot.
Gambol hates Joker and makes it vocally and visibly obvious, he wants to be seen and respected as an original gangster more than a wise guy so he's very loud and arrogant, being the first to threaten Joker in front of everyone instead of just quietly killing him. This allows Joker to play him like the cops and even Batman for a time by turning his predictable acts of aggression on him.
The Chechen doesn't love Joker, but he's willing work with "freaks" if it makes his life easier, and so he vocally makes it clear he'll cooperate, but this ultimately leads to him being played by Joker like the clown robbers since Joker can smell his willing duplicity.
The one actual wise guy is Maroni, he's quiet and observant. He takes in the measure of others without letting them get any of him. Since he neither opposes or offers Joker anything it's impossible for Joker to play him.
So, after killing Gambol, Joker meets with Chechen and asks "where's the I-talian?" this hints Joker had plans to do him and Chechen at once, but Maroni's getting out of dodge once he figured where it's all headed, so Joker plays Dent to go after him to get rid of the last loose ends just like the last clown who got wise to the process of elimination at the bank.
tl;dr Joker always has some form of plan, they just involve making himself seem less involved or intentional than he is so no one knows what it is and how to stop it until he's done.