How to break bad habits?

The first step in overcoming this material conditioning is of course to recognize the bad habits themselves. This recognition should be accompanied by sincere regret followed by firm resolve to give up the habit. But often we find that despite being aware and regretful for their habits, many people are unable to avoid their sinful tendencies, because of the lack of proper effort. It takes great commitment sustained over time to accomplish the result.

Srila Rupa Gosvami gives us the formula for accomplishing it:(Nectar of Instruction verse 3)

utsahan niscayad dhairyat
tat-tat-karma-pravartanat
sanga-tyagat sato vritteh
shadbhir bhaktih prasidhyati

i.e.Enthusiasm, determination, patience, following regulative principles under the guidance of saintly authorities, and avoiding bad association.

The particular methods for addressing specific bad habits may vary, but these are the fundamental principles and I would like to particularly highlight two key factors that support all the others, and help us stay on track until we completely break free — good association and adopting strong daily practice of devotional activities.

Submission and developing attachment to the good preceptor is the most compelling force that gives leverage to overthrow our deep-rooted bad habits. Srimad Bhagavatam describes, that even lowborn and uncivilized people can come to the highest perfection of life. Once again how we can develop that submission and attachment is by valuing and appreciating very deeply the association of such saintly devotees.
One way of practical expression of such submission is to take up strong devotional practices, (daily chanting, scriptural study etc) which themselves give us determination and keeps us enthusiastic. But beyond that they attract the mercy of the Lord, Who alone can ultimately cleanse all material contamination from within our hearts (SB 1.2.17:). Without the accompanying cultivation of theistic knowledge and positive spiritual practices, other methods to counteract bad habits, as we often see around us, would at best effect a temporary change. Sooner or later the living entity will once again become susceptible to and overwhelmed by material energy.
In short, the process of retraction of bad habits can be summed up as follows: Recognition, Regret, Rectification, and Reinstatement - aided by saintly association and devotional practices.

----As explained by HH Romapad Swami.