How do you quit drinking and smoking?
There is no magic involved. It really depends on your determination on what you want controlling your life, a box of leaves rolled up in paper, a bottle of liquid, or you. It won't be easy because tobacco alters the chemistry in your body and alcohol gives you the illusion of escape. You'll have to have control over your own body's cravings. The people I've known who successfully quit all came to a point in their life that they were disgusted with themselves for letting mere chemicals dictate their choices and they stopped. "All things are lawful for me, but all things are not helpful. All things are lawful for me, but I will not be brought under the power of any" (I Corinthians 6:12). Oh, they battled the cravings, but it was their determination to end it that did it. Even when they slipped, they just started again and were usually more successful the next time around.
So it really comes down to self-control. Such is a part of the Christian's life. "But also for this very reason, giving all diligence, add to your faith virtue, to virtue knowledge, to knowledge self-control, to self-control perseverance, to perseverance godliness, to godliness brotherly kindness, and to brotherly kindness love" (II Peter 1:5-7). "Diligence" is an interesting word in the Greek. It translates the word spoude, which means to hurry or do quickly; to work hard and do your best; and to be eager, devoted, or willing to work. It carries all three meanings at once. So the first step is to approach the problem with diligence. Quit cold-turkey before you have a chance to change your mind. Work hard at it, giving your all to not give in. And be devoted to success.
The second step is faith. You have to believe that this is the best choice for you. If you aren't convinced that it is really harmful to you, you won't stick with it. You will constantly give yourself excuses to compromise just one more time. Most importantly, you have to believe that what God says is true and that these drugs are harmful to you, such as God's warning that "Wine is a mocker, strong drink is a brawler, and whoever is led astray by it is not wise" (Proverbs 20:1).
The third step is virtue. It means doing what is right. You can't go by your feelings or your cravings. You have to see the right course and walk the right path. There will be many times you will want to drink or smoke, but you have to fix in your mind that it doesn't matter, you will chose to do what is right and that doesn't include ruining your health and dimming your mind with drugs.
The fourth step is knowledge. You need to learn. You need to learn about why these drugs are dangerous, why God says to stay away from them, and what it is that triggers your cravings for them. You also need to learn better things to do, instead of drugs. For example, if loneliness triggers your desire to drink then learn a better way to cure your loneliness that doesn't involve drugs or other sinful behaviors.
Next is self-control. You have to exert control over your behavior, understanding that in all things you have choices. "But I discipline my body and bring it into subjection, lest, when I have preached to others, I myself should become disqualified" (I Corinthians 9:27).
Next is perseverance, the ability to continue despite what happens. There are going to be times when you get tired of the struggle and just want to give up. There are going to be times that you succumb to the temptation in moments of weakness. Perseverance is picking yourself up and continuing on anyway.
A step that so many neglect is godliness. If all you do is focus your entire time on removing sinful behavior from your life, you'll never succeed. There has to be something better that replaces it. "Godliness" is the concept of being holy, understanding that you are someone special, set apart by God to do special things. "Therefore gird up the loins of your mind, be sober, and rest your hope fully upon the grace that is to be brought to you at the revelation of Jesus Christ; as obedient children, not conforming yourselves to the former lusts, as in your ignorance; but as He who called you is holy, you also be holy in all your conduct, because it is written, "Be holy, for I am holy"" (I Peter 1:13-16).
What locks these things into place is brotherly kindness. When you can see that you are not doing this just for yourself but also for those you care about, you will have more motivation to continue to do what is right. When you reach a point that you can pass on your desire to live free of chemical controls and in service to God, then it will become more real to you. Plus, focusing your life of caring about other people will get you out of the mode of feeling sorry for yourself which often is a roadway back into using chemicals.
Finally, the chief thing is to grow your love: your love for yourself, your love for those around you, and most importantly your love for God. It is just this reason that Paul used to tell husbands how to care for their wives properly and not sin against them. "So husbands ought to love their own wives as their own bodies; he who loves his wife loves himself. For no one ever hated his own flesh, but nourishes and cherishes it, just as the Lord does the church" (Ephesians 5:28-29). Love then provides the strong desire to remain in righteousness.
You might notice that all of these steps work in every area where a Christian is striving to improve his life. "For if these things are yours and abound, you will be neither barren nor unfruitful in the knowledge of our Lord Jesus Christ. For he who lacks these things is shortsighted, even to blindness, and has forgotten that he was cleansed from his old sins. Therefore, brethren, be even more diligent to make your call and election sure, for if you do these things you will never stumble; for so an entrance will be supplied to you abundantly into the everlasting kingdom of our Lord and Savior Jesus Christ" (II Peter 3:8-11).