If there's one thing I've learned about letting go of old habits and replacing them with new, healthier ones, is that the last thing you do is condemn and hate the thing you are looking to let go of (whether it be cigarettes, over-eating, television, alcohol, weed, drugs)... The reason being because whatever it is you are trying to let go of, has most probably served a crucial purpose in your life at some point.
For example, when I quit smoking cigarettes, the time that actually stuck was when I wrote the story of our meeting, the circumstances that brought us together, my reasons for trying them, what purpose they served then, what purpose they served over the years, and what purpose they were serving in the present, as well as how they were affecting me in the present, and then gratitude for them. Cause chances are, whatever you are trying to let go of has been a companion, a silent witness to all the sh*t you've experienced over the years. And then a good-bye, a grieving for them as you write about how they are affecting you now, I am assuming that if you are trying to let go of some habit, then it is having adverse affects on you in one way or another (guilt, shame, compromised health and immunity, etc). And don't be surprised if you cry during any of this process.
After you say good-bye to whatever it is you are trying to let go, be clear about what you will do instead that feels healthier and more aligned with body, mind, heart, and spirit health that can also serve the purpose that your vice served. So, for example if the purpose of your vice was relaxation, (but chances are when you first started it served a completely different purpose), what can you do for yourself that will relax you now (with special importance to doing this new thing during the times you would normally smoke or engage in your habit)?
I recommend engaging your senses to aid in this process. For example, if you were a nighttime smoker like I was, during the time you would go and smoke, light incense or a floral scented candle, create a sacred space in some part of your house, so you can enjoy your alone time if you normally smoked alone, read a page from a sacred or inspirational text, take a bath, write in a journal, paint, listen to or play music, rub a calming essential oil on your neck, make a yummy cup of tea, meditate, do yoga, whatever it is, let it be something you enjoy, something you can look forward to. Implement a new ritual that is loving, healing, and brings a sense of peace.
And if you start smoking again, or start whatever it is you were trying to let go of, be gentle with yourself, be loving, be kind, treat yourself as you would your best friend. Write your way through it, seek support from a loving friend or professional helper, and notice any tendencies to condemn yourself harshly, judge or criticize yourself, notice what it is you are saying and feeling toward yourself, notice and choose what kind of a relationship you would like to have with yourself moving forward... More loving, more gentle, more patient, and begin now. Wrap yourself in a loving embrace, pray for divine intervention to help you fulfill your intention, and forgive yourself. And when you're ready, go through the process of letting go once more. And believe in yourself, and if you don't believe in yourself, decide that you are ready to now to be the kind of person who does believe in herself. A wonderful prayer I heard from Dr. Christiane Northrup was “Dear Beloved, change me into a person who... lets go of what is no longer in service of her mind, body, heart, and spirit health (or you fill in the blank).” And surrender to your humanness, praise your spiritualness, and enjoy your feeling of FREEDOM when you let go!