What’s the best way to convince a non-believer that God exists ?

You cannot convince someone that God exists a part of their own worldview. Atheism is a rational because there is absolutely no proof that God does not exist well everything in creation points to the fact that there is a creator. But just try telling someone who is stuck in a materialistic mine says that. I would point them to the testimony of the great biologist Francis Collins who went from atheist to Christian by a process of reason.