I can only think of three prerequisites:
FIRST, YOU MUST BE COMPLETELY WON TO CHRIST YOURSELF.
You've got to be a Christian before you can help someone else become one, and I don't mean just a half-committed one. You've got to be excited about the gospel of Christ before you'll ever get anyone else to be excited about it. If you want to sell a product in the business world, then you have to know the product and be excited about how great it is before anyone is ever going to buy it. The same is true with the gospel! The gospel is the best "product" imaginable. Everyone can afford it and everyone needs it, but if we don't talk to the lost and try to "sell the product," so to speak, they won't be interested. They won't even know that it's available to them! If we don't show them how great it is to be a child of God and to have one's sins forgiven, then how will we ever get people to pay attention? If we don't have the peace of God radiating from our lives, why would anyone want to become a Christian like us?
SECOND, YOU MUST BE DETERMINED AND PERSISTENT. We often quit too soon in trying to convert people. Statistics reveal that the majority of insurance sales are made after the potential client is contacted five times by the insurance agent! Does that tell you why we do not win more souls? Generally we might ask someone if they want to go to church with us and if they say "no," then we never approach them again! Friends, ask again and again! It will show your determination and persistence. It will show that person that you're really interested in the gospel and the church. Think about how determined God was to save us. He did whatever it took--even the death of Christ. We must be determined and persistent because we're not selling insurance or trying to unload vacuum cleaners on people. We're doing something infinitely more important! People can go to heaven without insurance and without a vacuum cleaner, but they can't go to heaven without the gospel! We must be determined to get them to see their need for the gospel--God's power to save man (cf. Rom. 1:16). Don't be discouraged when someone says they're not interested in the gospel, because things happen in life and people sometimes change. Someone who says "no" today might say "yes" next month or next year. In the meantime, the more they see of you living a pure and devoted Christian life, the more likely it is that they might change their mind in the future!
THIRD, YOU MUST HAVE A PLAN.
I am told that the most successful form of evangelism in today's world is friendship evangelism. I have both read and heard that a majority of those who are converted from the ways of the world first became friends with a member of the church and that friend actively pursued them for Jesus. That friend cared enough to teach them the truth! Remember, your friends are always your best prospects. The advantage in trying to convert your friends is that you already have things in common with them. You know them, and it's not like talking to a stranger. They trust you (unlike strangers) and hopefully respect you. All of these things are important and will increase your chances of being able to reach them with the truth of the gospel.
How does friendship evangelism work? Well, there isn't just one method; there are many ways to approach your friends with the gospel. I suggest you try some of the following ideas:
What's important is that you try to reach your friends for Christ with an approach that works for you! You'll get better with practice (like everything in life). You'll say something and then realize later that you could have said something better. This happens to all personal workers. Modify your plan as you learn and grow, but keep sowing the seed and trying to save souls!