"The fear of the LORD is the beginning of knowledge, but fools despise wisdom and instruction." Proverbs 1:7
Once you've stopped having this personal conversation with your potential new convert, what do you do next? You have to know about the Gospel to be able to preach it. There aren't too many verses about this from Jesus and Paul, but this one from Proverbs that I find very important in this discussion. Proverbs 1:7 states, "The fear of the LORD is the beginning of knowledge, but fools despise wisdom and instruction." So, this starts by saying that your knowledge starts by confessing your love for Jesus, but you cannot continue if you lack or don't want to receive instruction. You cannot expect there to be a new Christian among you, if you cannot take the time yourself to bring in some knowledge to show other people, that is just foolish!
This does not meant that you have to know every last detail about the Gospel, but you need to have a general idea, and a motive to keep on learning. If you cannot answer you new friend's questions, don't pretend like you know the answer, take one of these two approaches. The first option is to open that Bible in your bag or tucked under your arm and try to answer the questions together. The second option is to direct your friend (and yourself) to your pastor who can probably answer your questions. Once you have brought this knowledge to one new recruit, or many potential converts, you need to make sure that you have the ability to stand your ground against those who are going to try to cause you to fall, or the new Christian to lost their faith right away!