If your friend is not a Christian, do not take his spiritual condition lightly. Every human being who has ever lived will one day face God in judgment. That certainly includes you and your friend. You want to be right with God when you stand before Him in eternity, and you want your friend to be ready also. II Corinthians 5:10,11 states - "For we must all appear before the judgment seat of Christ, that each one may receive the things done in the body, according to what he has done, whether good or bad. Knowing, therefore, the terror of the Lord, we persuade men." If you are concerned about your friend's spiritual condition, you will pray to the Lord about him. It helps to talk to God about a friend before you talk to a friend about God. Colossians 4:2-4 teaches - "Continue earnestly in prayer, being vigilant in it with thanksgiving; meanwhile praying also for us, that God would open to us a door for the word, to speak the mystery of Christ, for which I am also in chains, that I may make it manifest, as I ought to speak."
If your friend is not a Christian, be a good example to him. It is an undeniable truth that you will not lead someone to Christ if you don't first live as a Christian yourself (cf. I Tim. 4:12). In addition to guarding your influence carefully, you will also speak a good word to your friend from time to time about Jesus and His church. Some of the best sermons are only one line long. One sentence might start him thinking.
If your friend is not a Christian, invite him into your home for a meal and spend time with him. Jesus ate with sinners in order to influence them for good and teach them (e.g., Matt. 9:10-13). Getting to know your friend better is important if you hope to win him to Christ. If he needs help, be there to provide it if at all possible. "My little children, let us not love in word or in tongue, but in deed and in truth" (I John 3:18).
If your friend is not a Christian, give him religious literature. Give him a tract that is relevant to him. Share lessons from AudioEvangelism.com with him (or any other website that contains good, reliable Bible teaching).
If your friend is not a Christian, tell him what great things God has done for you and why you are a Christian. In Mark 5:19,20, Jesus instructed the man whom he had just cast many demons out of - "'Go home to your friends, and tell them what great things the Lord has done for you, and how He has had compassion on you.' And he departed and began to proclaim in Decapolis all that Jesus had done for him; and all marveled." Tell your friend how blessed you are to be a child of God (and show it in your daily attitude). Invite him to Bible class and worship, and pick him up and bring him with you. Introduce him to as many brethren as possible.
If your friend is not a Christian, invite him to study with you. If you don't feel competent enough to lead such a study, ask a preacher or an elder to assist you. If your friend says "no," ask again in the future. If he says "yes," seek to teach him the truth of the gospel in love. Keep praying for him and working with him. If he obeys the gospel and becomes a child of God, continue praying for him and encouraging him in his growth. He will need your support.
Before the Lord ascended into heaven, He said - "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things that I have commanded you; and lo, I am with you always, even to the end of the age" (Matt. 28:19,20).
Dear listeners, although you may never travel halfway around the world to evangelize, you can and should and must reach out to your friends here and now! Don't be ashamed of the gospel (cf. Rom. 1:16), but sow and water diligently and God will bring forth the increase. If you really love your friends, you have no other choice!