Becoming a Christian is one of the simplest and yet one of the hardest things that anyone can do. It is easy because God does not ask us to do anything. In fact, he even asks us not to do anything - only believe!
Perhaps this is what makes it so hard - the fact that it is so easy. Why isn't Christianity like every other religion? Shouldn't we have to try to please God by improving our act? Shouldn't we, at the very least, have to go through some kind of ceremony or join a particular church? No, we don't become a Christian by doing things like that. It is true that believers get baptised. But even baptism is performed after a person has become a Christian: it is not the act, which makes us one. So what we do to become a Christian isn't something done outwardly, but is something that is done in the heart.
Actually there are 4 steps involved in this process:
STEP #1 to becoming a Christian
The first step to becoming a Christian is to admit what we are. Yes, this is the hard part. Who me? A sinner? We think ourselves to be about as good as the next person. We excuse ourselves by comparing personal sin with those who are guilty of worse things than we have done.
But self-justification is a delusion. It is a delusion because all of us will stand before God one day. The simple fact is that we all fall short of God's standard. And this is what God is asking us to recognize in our heart. When we finally do acknowledge our sin we are close to becoming a Christian.
STEP #2 to becoming a Christian
This brings us back to the point of it all. How do we become a Christian? We must believe! It's basic. How can anyone pretend to be a Christian if he doesn't even believe that God exists? However, it means more than that. We must believe that Jesus Christ is the Son of God. What this means, in effect, is that Jesus Christ carries all of the authority and power that God does. He is as much 'God' as the Father is God. Do you believe that? Do you realize that you are making Jesus Christ your God?
STEP #3 to becoming a Christian
However we are fooling ourselves if we think that our way of life need never change. When the preacher says, "we are saved by grace" (undeserved mercy) - by God's free gift without having to do anything for it - that does not mean our life can go on the same as it has been going.
On the contrary: becoming a Christian involves a complete turnaround in our deepest motives. Its called repentance; it is a decision to turn away from self-centered sinful living.
STEP #4 to becoming a Christian
Finally, in order to become a Christian, we must receive. Again it seems so simple that it's almost too hard to understand. What do you mean, receive? A Sunday school teacher once told his class of children, "I've got a dollar in my pocket and you can have it if you want." Then he asked, "Do you believe that there's a dollar in my pocket?" All the children put their hands up. They believed. "Well," he said, "who believes that whoever comes up to the front will get the dollar?" They all put their hands up again. They believed. "OK," he dared. "Come on up. The first one to come will get it." None of the children moved. Was this for real? Would he actually give them a real dollar?
A small boy suddenly stood up and walked to the front of the class. The teacher pulled his hand out of his pocket and gave him the dollar - yes, a real dollar. He received.
So it is, that although we have believed, there remains one thing to do in order to become a Christian. Many people believe but are not yet saved. This is because the last step is to actually ask Christ into our life. These are the 4 steps to becoming a Christian.
If you do these things the Spirit of Christ will come into your life; you'll enter into a living relationship with Him, and receive the legitimate right to be a son or daughter of God.
Father in Heaven,
I realize that my life is sinful and selfish in your sight, and that as a result, I am very far from you.
But I believe that Jesus Christ is the Son of God, and that he died for me that I might not be rejected if I asked to be received into a relationship with you.
Therefore I confess my sin and ask that you forgive me. Not only for the things that I have done, but for my whole sin attitude against you I repent - I change my mind. With your help I determine to turn away from my old way of living.
Now, I receive Jesus Christ into my life as my Savior and Lord. I believe that through Him I have eternal life, and entry into your presence and, even from today, a living relationship with you.
Taken from bibleforums.org