Hey friend of mine! ^__^
The only way to prove that God doesn't exist is to contradict what they believe and preach. For example, if someone says that God is responsible for creating the beauties of the world such as mountains, tell them that it's PROVEN that convergent boundaries are responsible for that. If they say that God is responsible for life and how it expands, tell them it's PROVEN that God has nothing to do with life because it creates itself on a regular basis. For example, when two humans of different gender have unprotected sex and the female become pregnant and has a baby, the parents were responsible for the life, not God. If they try to say the Bible is proof, tell them if that's the case, The Three Little Pigs could be considered real too because readers have never seen God and friends in person, and you can't sense God with your five senses. That's why he doesn't exist to me. Also, I believe we came into existence because of forever-abundant energy. Energy has ALWAYS been, and if a religious person tells you that God created energy, contradict them by telling them that for God create to energy, he NEEDS energy. See, even if the supernatural was real, it would still need some form of energy to exist because no force can simply "not exist." It isn't possible. Even in an area where you see nothing, there's a large amount of matter present.
EDIT - 7:05AM: By the way, SOMETHING created that universe, and do you know what that something is? It's energy, something that NEVER creates or kill itself. See, because energy is always abundant and it creates things like gravity, friction, and atoms and such, chances are, it could create things like new planets. Gases are made up of molecules and molecules are made up of energy, and you never know, energy could have created the sun which is the fuel for all life.