Change starts with salvation through personal faith in Christ and this is where you must start with your friend. Any other kind of change will be either short-lived or incomplete at best. Biblical change (change from the inside out that effectively reaches into all areas of one’s life) is always a product of spiritual growth through an understanding of Scripture.
In helping your friend, may I suggest a careful study of the ABCs For Christian Growth, Laying the Foundation series on our web site in the “Bible Studies / Spiritual Life” section. This covers the issues of salvation, assurance of God’s provision in dealing with sin and many other important issues. The second section of the study is devoted specifically to the spiritual principles and disciplines that lead to change from the inside out that comes from steady growth in Christ.
Further, it is important to realize that true change is usually slow. It takes time through growth in the life-changing promises and principles of Scripture. The Bible says, “As newborn babes, long for the pure milk of the Word that you may grow unto salvation (deliverance)” (1 Pet. 2:2). It also says, “But grow in the grace and knowledge of our Lord and Savior Jesus Christ” (2 Pet. 3:18). But of course, the first step is to win your friend to a real personal faith in Christ. The material in the ABCs will help you step by step.
This will involve a lot of reading on your part, but this should be beneficial not only in your own life, but also in your witness to your friend. Obviously, this is a spiritual battle and you need God’s enablement, so pray faithfully for your friend. Effective ministry is the result of prayerful dependence on the Lord.