In this article, I must assume that you are already questioning the tenets of the faith that you were brought up in, and I must encourage you, this is healthy behavior. I think that no matter what beliefs you hold, whether they be religious, spiritual, scientific, or anything else, should always be challenged. If you challenge what you believe and decide you no longer believe it, that is called growth. And if you challenge what you believe and it comes out intact, you have made your belief stronger, and have discovered a new way to help share that belief with others.
Things You Will Need
There are not many "materials" that you will need. However, I do encourage anyone that thinks they might be an atheist to have and read religious texts. You should not reject something you know nothing about.
Open your mind - This goes without saying of course, and the reasons for it are explained in the introduction. If you are truly unwilling to challenge the beliefs you already hold, you will not be able to learn anything new.
Read the bible, quran, or any other holy book, or all of them - In order to make an informed decision on whether or not to be an atheist, you must learn about the ideas and philosophies you will reject by being an atheist. A misinformed atheist is no better than a misinformed christian. Misinformation can lead to bigotry and discrimination, and in order to be a good representative of atheists, you do not want to come across this way. If you even decide to try to help others become interested in atheism, it helps when you know their faith and can speak about it as well as they do.
Be willing to constantly question - You must be willing to constantly question what other people tell you. Also, and usually more difficult for most people, you must constantly be willing to question yourself. Seek truth, not satisfaction. The truth is not always what you expect, or what you want. But the truth, backed by facts and observation, is more powerful than just hearing what you want to hear.
Be humble - Many atheists can be guilty of coming across as arrogant. It is ok to be convinced, based on your open-minded explorations of the facts, that you are correct. In fact, if you have doubts about your atheism, you would more accurately be described as an agnostic. But just because you are convinced does not mean that everyone else should be, so you must not judge them or think yourself better than them.
Live a better life - Some religious people believe that morality comes from god, and that without god civilization would devolve into a disgusting mess of murder, rape, and destruction. Live your life in a way that proves this is not true. Be good to your fellow man, donate to charity, volunteer your time, be a moral person. Morality can come from any number of sources, depending on who you are, so prove that atheists are just as moral as anyone else by living a good life in the service of other people.
Seek out others - Seek the knowledge of others who have gone before you. Many prominent atheists have already had the ideas that you are now discovering. Read books by Christopher Hitchens, Richard Dawkins, Sam Harris, and others. However, while doing this, avoid at all costs the dangers of group-think. Read the writings of prominent religious figures as well. Let them challenge your beliefs. Consider what they say and understand why you reject it. You will always be a more informed and well rounded person if you seek information from all sides, and understand why you accept or reject that information.
Being an atheist is not necessarily a lifestyle choice. It is possible to choose to be a private atheist who believes there is no god, but does not have a public discourse on the matter, and that is fine. I have written the above steps with the expectation that you might be the kind of person who wants to share their ideas with others, to help them achieve the peace that I have achieved by not always worrying that a god is looking over my shoulder all day. However, I must again stress the importance of living a better life once you have made that decision. My own source of morality comes from the idea that this life we have is the only one we have. With that in mind, I do everything I can to try to help people enjoy the life they are living. This sometimes means NOT asking them to question their religious beliefs. Some people may not be ready to do so, and you will only cause stress or anger by asking them to. Be thoughtful and selective if you choose to try to spread your beliefs, just as you would ask of a religious person trying to spread theirs to you. And if you notice you are making someone uncomfortable that you might be trying to spread your beliefs to, be courteous. I'm not asking that you should give up your right to free speech in the interest of someone else's comfort, but there is a time and a place for everything. Speak you mind boldly, be confident if you have come to your decision with facts and reasoning, but do not proselytize to others if they are not interested. And always, always accept criticism will the knowledge that you are being given an opportunity to learn from it.
Tips & Warnings
Becoming an atheist can be taxing emotionally. You risk the rejection of friends and family, and ridicule from many people in your community. However, in my own life, I have found that seeking the truth at the expense of ridicule has always, in the end, been more rewarding fulfilling.