Every habit I've managed to get rid of, it was by substituting better habits. Making routines and slowly weeding out the bad ones.
Currently, I need more physical activity in my life. I spend a lot of time on the PC, so I've taken out my standing desk. I'm going to start taking my camera on weekend walks when the weather is nice, too. I'll add in other things once I've made these habits stick. Small goals are better, IMO.
So, do you have a habit you want to kill or reduce? Or, have you managed to change any habits? If so, by what process?