Without God, morality would be impossible. There must be a Lawgiver (God) who developed and stands by moral law. A universal moral law cannot exist accidentally. There must be a basis behind it—namely God.
In my opinion, the moral argument for God is the strongest! There is no way getting around morality without God. Moral absolutes must define what is good and what is bad. When morality is relative, then anything can be considered justifiably good.
Simply talk about how Jesus changed your life. No one can argue with your experiences. Make God real as you talk about how he touched and impacted your life. I’ve never seen someone debate whether or not God actually redeemed someone’. Just talk about why Jesus is King of your life.
Resources for Researching Good Theological Questions
Standtoreason.org — Greg Koukl trains Christians to think more clearly about their faith. He helps them make an even-handed, incisive, yet gracious defense for Christianity and biblical values.
Reasonstobelieve.org — Hugh Ross, the founder and president, completed his undergraduate degree in physics and graduate degrees in astronomy. He wrote the amazing book Why the Universe Is the Way It Is
I also recommend Tim Keller’s book The Reason for God