How do you convince someone to stop a bad habit?

Let him realize the good effects of stopping a bad habbit and help himrealize what he/she is missing.

i would recommend something new for that person forexample going to cinama for someone addicted to a drug to interupt that person

I try to demonstrate all the bad effects of the habits and show all the best if the person stop the bad habit.

I try to convince the person in being rational and after i will try to touch the person in their feelings to prove that the benefit is real and the person could arrive to stop if he wants.

the approach will be simple as you first open conversation with that person and when the person feels comfortable on the conversation... you open the topic by explaining the bad habit what it can give a bad impression without even knowing the person, and help him or her out by guiding her with solutions.

First it's better to understand the history behind that habit regarding why and how it started. Because we are in no position to judge an individual because of his habits, let alone make them stop or change it.

At a later stage, maybe help the person list out the pros and cons himself/herself and help them realize themselves that this certain habit may be doing more bad to them than good. 

to convince someone to stop a bad habit .I show him the negative side of this habit

Traning on the right or recommended behavious besides counseling where necessary

At first you have to clarify why its a bad habit and its effect to the person or his job and its consequences to their life. 

you can help someone to stop a bad behavior by highlighting on the implications and consequences of the their behavior and also by being a role model [living by example] and by modeling alternatives or means of such habits they display

1. Search for the causes of this common misconduct

2. Tell him to damage this habit

3. Help him not to do it again