Use God's moral Law(The Ten Commandments) to point him to Christ

Gal 3:24
Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.

Reason with him just how desperately wicked he is; in other words what a monster he is.

Jer 17:9
The heart is deceitful above all things, and desperately wicked: who can know it?

Ask him if he has kept the Ten Commandments:

-lieing (you could give an example where you explain to him that even parents telling they're children that santa is real is a lie; it's an abomination in the eyes of God)
-stealing(a pen, pencil, chocolate bar even count)
-hated (hatred is murder in the eyes of God)
-used God's name in vain (said oh my blank or Jesus with some cuss words; said Jesus is my homeboy or that Jesus is just "alright with him", etc.)
-dishonored his parents (yelled back at them, didn't take out the garbage when they told him to)
etc.

Reason with him about how God has given him a conscience; he has no excuse.

Romans 2:15
Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;)

Reason with him about seriousness of these crimes

explain to him the reality of hell and how he deserves it for his crimes (sins)

Then preach the good news of the gospel (the death, burial, and ressurrection of Jesus Christ)

1 Cor 15:1-3
1Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
2By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
3For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
4And that he was buried, and that he rose again the third day according to the scriptures:

2 Corinthians 5:21
For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.

Explain to him his need to repent(turn from sinful ways to God) and believe on Jesus Christ

Repent:

Luke 13:3
3I tell you, Nay: but, except ye repent, ye shall all likewise perish.


Believe:
Rom 10:9
9That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.



That is just a brief outline.


Remember this it is the Holy Ghosts' job to convict of sin, the Father who draws and the power of God unto salvation.

John 16:7,8
7Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you.
8And when he is come, he will reprove the world of sin, and of righteousness, and of judgment:

John 6:44
No man can come to me, except the Father which hath sent me draw him: and I will raise him up at the last day.

Romans 1:16
For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.


You are just a messanger.

Rom 10:14,15
14How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher?
15And how shall they preach, except they be sent? as it is written, How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things!

Mark 16:15
15And he said unto them, Go ye into all the world, and preach the gospel to every creature.

Thus because you are the one who cannot save, the one who cannot make your brother see yourself as lost, you must tell him the message and rely on God in prayer.

Luke 19:10
For the Son of man is come to seek and to save that which was lost.

Until your brother sees himself as lost(a hell-deserving sinner), he is not ready to be saved.

Pray, weep, mourn. Tell him the message, warn his wretched soul and pray and pray!

May the Lamb that was slain receive the reward of His suffering!