1st of all we have to realize that we have a bad habit and we have to quit it. Unless and until we realize we are hampering our future we can't change.
Ok now how you will change it or avoid it? If you look closely you will find that most of the bad habits are easily available. For an example if you smoke cigarettes are always present with you or if if you drink too much then you have a good source of it.
So 1st of all you have to change it and make it hard for you to reach there. Suppose you for cigarettes you have to walk 15 min and have to pay 10 times more to buy it. Gradually you will notice that you are consuming less no of cigarettes.
2ndly you have to find out which triggers you to do that. I mean if you smoke then which provokes you to smoke and drink . And you have to eliminate that source .
Definitely you will see positive results.