Present the gospel
So, you have started the conversation, and have made the person realize that they are dead in their sins and hopeless without grace given directly from God (a savior). Now what? How do you now present the gospel to them? First and foremost always remember, the Holy Spirit will tell you what to say. Below are some ways which have worked for me in the past, but say whatever you feel God is leading you to say.
The Alarms of Heaven
Even though the person realizes that without help from God, they are going to spend an eternity in hell, I still like to give examples to help them understand what position they are in.
One example I love to use is the 'alarm example'. Pick an article of clothing the person is wearing (like a hat or a shirt) and ask them what would happen if they had walked out of a store while a security tag was still on the shirt. The alarm would go off unless one of the employees removed it. We can think of heaven in a similar way. Our sins are the 'security tag' and if we try to walk into heaven with them on, they will set off the alarms. Sin can not enter heaven, so someone must remove our security tag (our sins) in order for us to enter the Kingdom of God. From there, explain the gospel.
Presenting The Gospel
When witnessing, many people get scared when it comes time to actually sharing with the person the gospel and what Jesus did for them. Don't be! Someone must have explained it to you, and you understood it, so you do know how to present the gospel, because someone did it for you.
Simply explain that Jesus came, lived a perfect life, died for our sins and took the wrath of God on Himself, then rose from the dead three days later, showing that he had conquered those sins for us. No other 'religious' leader did it, only Jesus Christ. John 14:6 says "I am the way, the truth, the life; no one comes to the Father but by Me." Jesus did not say He was a (singular) way to heaven, or a (singular) way to God. He said He was the only (singular) way! People must understand that trusting Jesus Christ is about putting their faith totally in Him as the one and only way, not as a possibility that happens to work for them.
I was once talking to teenage girl who, when she heard the gospel, got extremely excited. She said, "Jesus died for all my sins!" I couldn't believe how it appeared God was working on her heart! Needless to say I was excited. So I asked her, "Would you like to trust Jesus Christ as your savior right now?" She answered, "As mine, yes."
Whenever you hear someone say something which implies the 'it works for me but not for you' attitude, always clear it up. Don't ever let someone believe they are excepting Christ when they aren't willing to admit He is the only path to heaven and to God for eternity. If Jesus was willing to go through the pain of giving us the only path to heaven, we must be willing make sure people understand that he is the only way.
So I asked her, "What do you mean by as mine?" Needless to say, she answered, "Well Jesus can work for me, but all other religions are still right and lead to heaven too." Once she said that I knew she was not ready to trust Jesus Christ. I could have kept going and still encouraged her to accept Christ. But, what would I have been doing? Lying to her.
People must understand the commitment they are making when they commit their life to Christ. This young woman did not understand that commitment.
A Life Changing Decision
Not only must you keep in mind when presenting the gospel that the person must understand Jesus is the only way to heaven, but you must keep in mind that the person must understand how serious trusting Christ is. Mark Cahill said, "Being saved is not about doing drugs, having sex, cheating on tests, and disobeying your parents. Then you get saved and do drugs, have sex, cheat on tests, and disobey your parents."
When someone tells me they want to put their trust in Jesus Christ, I always first explain to them the seriousness of the decision (I still encourage them to do it, but they must understand what they are doing).
Tell them that being saved is a life-changing choice. You will no longer want to live the same way and it will totally change your outlook on the world. Instead of making choices for you, you will want to make choices which glorify Christ, and live your life in a way that is pleasing to Him.
A young man once asked me, "So can someone who did drugs get saved?" What a perfect question to make this point! I explained to him that absolutely the person can get saved. But once he is saved, he would be driven to give up drugs, because that would not be an act which is glorifying to the Lord. And that by the faith in Christ, he would be able to give up his addiction and live his life in a completely different way. Does getting saved mean you will be perfect? No. But it does mean that we will want to strive for a life of perfection which will glorify Christ.
An example I love to use to make this point is using parents. If I am talking to teenagers I will tell them, "It is like this. You make mistakes sometimes, but you want to live in a way that will please your parents because they love you, and have provided and nurtured you for your entire life!" Once you are saved, you want to live to glorify Christ with everything you have.
I was once talking to some people on a beach boardwalk and a young man said he wanted to accept Christ. For about 10 minutes we talked about the seriousness of the decision he was saying he wanted to make. After talking to him about it I said, "So, are you willing to do that for God?" He was, and accepted Christ that night. Afterwards you could see the change in his face; you could tell had really just accepted Christ.
The $10,000 Ticket
One more example I love to use when actually presenting the gospel is the '$10,000 ticket' example.
Suppose you were driving down a highway and a cop pulled you over and gave you a $10,000 ticket. You go to court and are told you must pay the fine. But there is no possible way for you to come up with the money. A cop walks into the court room, drops a check for $10,000 on the judges table, and says he wants to pay the fine for you. Would you consider that cop to be gracious? Of course you would! Christ paid the fine for our sin when he died on the cross.