What are those bad habits you've developed since you've started coding in Cocoa?
I think making a list of bad habits and actively adding to it and, more importantly, breaking those habits is a good technique to produce your code quality. So start now, get your bad habits off your chest. Maybe other people share your bad habits.
Passing nil to arguments that call for NSError**, pure lazy.
Bad habit: Retaining my Java mindset.
My Java background leads me to obsessively check for a null before even thinking about doing anything with a variable, when I could be making use of Objective-C's ability to send a message to nil. (See: "Sending a message to nil?")
Instead of trying to preemptively catch a nil, I have to remind myself that Objective-C allows me to simply write code that gracefully works with return values of 0 or nil.