What is the starting point for purifying the soul?
Purification means to clean your soul of impurity. The Quran has mentioned purifying the soul in various verses but one should know that the basis and starting point of purification varies from person to person. For a person that is not Muslim, the first essential step will be to convert to Islam. For believers, it would be to become well aware of the necessity of purifying the soul. Clearly, pondering about why the world was created, what Allah’s objectives and purposes for creation were and why he appointed and sent the prophets and the like increase the notion of the need for purification.
The next stage is to repent from the past, make an effort to compensate for others’ rights he may have disregarded and to perform Allah’s (swt) commands which he has violated. Another step is to strive to abide by every obligation and prohibition one is aware of and to remain determined and persevere; this will result in Allah (swt) subsequently granting us additional knowledge which will help us in continuing our mission of the purification of our soul. Allah (swt) has given glad tidings by announcing his support for such servants that endeavor and struggle for his sake, and that he will strengthen them.
The concept of self-building has been referred to in the Quran as “purification” which means to cleanse the self from corruption and immorality. Purification is of great importance in the viewpoint of the Quran, thus we read in Surah Shams:
To a happy state shall indeed attain he who causes this [self] to grow in purity, and truly lost is he who buries it [in darkness]. 
Verses 19 of Surah Al-Fatir and verses 14 and 15 of Surah Al-Aa’lah also emphasize on the same matter. So purifying the soul is considered a praiseworthy and encouraged act in Islam, but the starting point in purification differs from person to person. For someone that is not a believer, converting to Islam is the first step required. According to akhlaq scholars these are the steps to purification: 1- Converting to Islam 2- Iman (Belief) 3- Immigration 4- Struggle for His cause. 
For one that has entered the safe fortress of Islam and is addressed by verses such as: “O you who believe, look out for yourselves”  and “O you who believe! Believe in Allah” , the first step is to become aware of the great significance of purification. After gaining this awareness the question: “Where should I start from?” comes to mind. Actually, it can be said that the person with such a question has surely finalized the first step; because he has reached the conclusion through his own intellect and thinking that “this world is not a place to live forever and all of these resources and the prophets of God were not sent in vain so we could live a life ruled simply by our carnal desires”. 
After this level (awareness), it is time for repentance and to make up for what has been lost; making up for whatever rights we may have disregarded concerning both people and Allah (swt). However, repentance must definitely be accompanied by a strong decision. Repentance from the past and a strong decision to move ahead. Hence, some akhlaq scholars believe in repentance to be the second stage  while others say it is to make a strong decision. 
Imam Khomeini has a phrase relevant to this matter:
“Resolving not to commit haram acts and to perform the wajib ones and to make up for what has been lost and determination to become intellectual and religious on the outside”. 
In the supplication of the day of Maba’th it says:
“Therefore I recognized that the most significant provision for someone seeking you is the sole determination to only choose you.” 
The next step after that would be to avoid haram acts and perform the wajib ones.
Ayatollah Bahjat has said in reply to the question “I have the intention to purify my soul, but don’t know what I’m supposed to do?”,
“Avoiding the haram acts is more than enough and guaranteed to answer throughout your whole life, even if you are to live for a thousand years”. 
So in this stage we are supposed to avoid the haram acts and perform the wajib ones to the extent of our knowledge. This very sequence provides the ground for Allah (swt) to bestow his grace and mercy upon us by granting additional knowledge in order to proceed further in seeking his nearness. Our progress in purifying ourselves is determined by the capacity of knowledge we obtain. Thus as long as we keep our end of the deal and correspond to our knowledge, Allah (swt) will grant us more and the process will continue. In a narration from the prophet (pbuh), he says:
“Whoever does what he knows, God will teach him what he doesn’t know.” 
This hadith is completely in line with what the Quran says:
“As for those who strive hard in us (our cause), We will surely guide them to our paths” .
Another thing that should always be kept in mind is that in every moment we are in movement; either towards light (guidance) or darkness (misguidance), what is important is to guide this movement towards the right direction.
For further information, please refer to Sayyid Mohammad Hossein Hosseini Tehrani, Resaleye Lobbol-Lobab, vol. 1, p. 87.
One reminder is that the answer given above is for average individuals; if you are looking for a higher leveled answer, let us know, but also inform us about your educational degree.
 التزکية التطهير من الأخلاق الذميمة
Majma’ul-Bahrain, vol. 1, p. 203.
 قد افلح من زگيها و قد خاب من دسيها
 Seyyid Mohammad Hosein Hoseini Tehrani, Resaleye Lobbol-Lobab, p. 55.
 يا ايها الذين آمنوا عليکم انفسکم
 يا ايها الذين آمَنوا آمِنوا
 Imam Khomeini, Chehel Hadis (Forty Hadiths), p. 76.
 Mirza Javad Maleki Tabrizi, Resaleye Liqa’ullah, p. 52.
 Chehel Hadith, p. 7.
 و لقد علمت افضل زاد الراحل اليک عزم ارادةيختارک بها
Mafatihul-Janan, The dua of the day of Mab’ath; Al-Iqbal bil-A’malil-Hasanah, p. 277.
 Be Suye Mahboub (Ayatullah Bahjat’s guidelines and prescriptions for self-building), p. 58.
 من عمل بما علم ورثه الله علم ما لا يعلم
Al-Mahajjatul-Beyda’, vol. 6, pg. 24; Biharul-Anwar, vol. 89, pg. 172; Al-Khara’ij, vol. 3, p. 1058.
 الذين جاهدوا فينا لنهدينهم سبلننا