Actually, I had the same experience, what I did is pray for her first, and talked with her about my faith in life, and how God love me and guide my life. I think which is important is that don’t argue with each other, keep a humble heart to listen to her, also know her needs and thoughts, then wait for God’s work in her heart. I’m very thankful God, He listen to my prayer and deliver my best friend, now she is a Christian and follow Jesus with her whole life.
How to share gospel to your best friend who do not believe in God?
Testimony is the first step, tell them the grace you got from God, then invite them to Church and join Bible study.
It is good that you have the mind to share gospel to your friends.
I also think that to pray for he or her will be the first step. And maybe share some praise songs to them. Also need to know the friends more. It is very important to be patient and not to be discouraged by their refusing. Keep pray for them and talk to them. God will work and when time come, the friends will be changed.
If we give our heart totally to the Lord the Lord will work through us according g to that person, we don’t evangelize but the Lord through us, All the glory to the Lord