1) Make sure you know what it means to be Muslim. The first and foremost rule of being a Muslim is believing that Allah is one and only one. Allah is the only god, the only creator and the Almighty. He is the only one you should be doing your good deeds for and the only who shall be worshipped. There should be nothing stood beside His place. Allah's messenger Muhammad (pbuh) is the messenger who is believed as the last prophet who came down to Earth and there will never be any prophets after that. Islam considers itself to be the natural way of all creation. That is, Islam is the original, perfect state of being. So, when a person "converts" to Islam, he/she is actually reverting to their own original nature.
Islam considers anyone who adheres to this state of being to be a Muslim, regardless of when or where she or he lived. For instance, Islam believes that Jesus was a Muslim, though he lived hundreds of years before Islam's historical founding.
Allah, the Islamic name for God, refers to the same God worshipped by Christians and Jews (aka the "Abrahamic" God). Thus, Muslims revere the prophets of Christianity and Judaism (including Jesus, Moses, Elijah, etc.) and consider the Bible and Torah to be divinely-inspired.
2)Read Islamic scripture. The Quran is the central religious book of Islam, believed to be the unadulterated word of God and the culmination of all previous Christian and Jewish scripture. Another very important religious scripture is the Hadith, the sayings and accounts of Muhammad. Hadith collections form the basis for much of Islamic law. Reading these holy writings will give you an understanding of the stories, laws, and teachings that make up Islamic belief.
3)Talk with an Imam. Imams are Islamic religious leaders who conduct religious services inside and outside the mosque (Masjid). Imams are chosen for their knowledge of Islamic scripture and their good character. A good Imam will be able to counsel you when deciding whether you're ready to devote yourself to Islam.
Note that the description above applies to imams of the majority Sunni sect of Islam. Imams have somewhat different roles in the minority Shi'a sect.
4)Say the Shahada. If you're absolutely sure you want to become a Muslim and fully submit to the will of God, all you need to do is recite the Shahada, a short oral declaration of faith. Be aware that once you have said the Shahada you are committed to following Islam for life. The words of the Shahada are "La ilaha illallah, Muhammadun rasulullah " This translates to "I testify that there is no other god but Allah, and Muhammad is God's messenger (prophet)." By saying the Shahada, you become a Muslim.
The first part of the Shahada ("La ilaha illallah") refers not only to deities from other religions, but also to earthly things which can take the place of Allah in your heart - wealth and power, for example.
The second part of the Shahada ("Muhammadun rasulullah") is a recognition that the word of Muhammad is the Messenger of God. Muslims are required to live by the principles of Muhammad revealed in the Quran - the Shahada is a pledge to follow these principles.
The Shahada must be said with sincerity and understanding to be binding. You can't become a Muslim just by pronouncing the words - the oral recitation is a reflection of belief that's held in the heart.
5)To become a legal member of the Muslim community, have witnesses present at your recitation. Witnesses are not strictly required to become a Muslim - God knows all things, so a Shahada said alone, with conviction, will make you a Muslim in God's eyes. However, to become legally recognized by the Muslim mosque, you generally must make your Shahada in front of witnesses - two Muslims or an Imam (Islamic religious leader) who is authorized to certify your new faith
You will never lie, steal, drink, do drugs, have sex before marriage or anything of the sort.
6)Wash yourself. Immediately upon becoming a Muslim, you should take a shower or bath as a form of purification. This is a symbolic act that signifies the washing away of the past and of emerging from darkness to light.
No one's sins are too grave to prohibit newfound purity. Upon making your Shahada, your past sins are forgiven. You symbolically begin a new life centered around striving to improve your spiritual state through good deeds.