What should I do after becoming a muslim?
Immediately upon becoming a muslim, you should take a bath or shower (i.e. Ghusl).
If able, you should then offer a two Rak’at prayer.
Then you must study and act upon the five principles (pillars) of Islam, and study and believe in the
six articles of Faith.
The Five Pillars of Islam (or the five basic duties of a Muslim):
[Sahih Al-Bukhari 1/7, Narrated by Ibn 'Umar]
Allah’s Messenger said: Islam is based on the following five (principles):
To testify La ilaha ill Allah wa anna Muhammad-ur-Rasul-Allah (none has the right to be worshipped but Allah and that Muhammad is Allah’s Messenger).
To offer the (compulsory congregational) prayers dutifully and perfectly (Iqamat-as-Salat, i.e. Salah).
Says al-Khattabi, "Basically, one's prayer does not suffice if he does not recite al-Fatihah. If one can recite neither al-Fatihah nor other portions of the Qur'an, he should recite at least seven verses of a similar meaning from the Qur'an. If he can not learn any part of the Qur'an (due to some innate inability, poor memory, or because it's a foreign language), he should say the tasbeeh (Subhaan Allah - Glory be to Allah), the tamheed (al-Hamdu lillah - All praise is due to Allah), and tahleel (La ilaha illal-lah - There is no God except Allah). It is related that he said, "The best remembrance after the speech of Allah is Subhaan Allah, al-Hamdu lillah, La ilaha illal-lah and Allahu akbar." This is supported by Rafa'ah ibn Rafa', who narrated that the Prophet said, "If you have something from the Qur'an, recite it. If not, then say the tamheed, takbir and the tahleel and then bow." [This hadith is related by Abu Dawud, at-Tirmidhi, an-Nasa'i and al-Baihaqi. The former considers it as hassan]
To pay Zakat (a specific charity paid yearly for the benefit of poor Muslims; 2.5% of wealth).
To perform Hajj. (i.e. pilgrimage to Makka).
To observe fast during the month of Ramadan.