Praise be to Allah.

The answer to this question is to see what the Messenger of Allah (blessings and peace of Allah be upon him) did when he sent out daa‘iyahs to call people to Islam. He (blessings and peace of Allah be upon him) sent the daa‘iyahs to call the people to Islam, and he taught them to start first of all with Tawheed or the Oneness of Allah, then the prayer, then zakaah, then fasting, then Hajj when the time for it came. He sent Mu‘aadh to Yemen and told him to call them first of all to Tawheed, belief in the Oneness of Allah. If they responded to that, then he was to call them to pray. If they responded to that, then he was to call them to give zakaah. He did not mention fasting and Hajj because when he sent Mu‘aadh, it was not the time for these acts of worship, as he sent him in Rabee‘ al-Awwal of 10 AH. There was still some time to go before Hajj, and also fasting. The Prophet (blessings and peace of Allah be upon him) in his wisdom did not want to spring all the rulings of Islam at once on those who were being called to the faith. This is part of the wisdom mentioned in the verse (interpretation of the meaning): “Invite (mankind, O Muhammad صلىالله عليه وسلم) to the way of your Lord (i.e. Islâm) with wisdom” [al-Nahl 16:125]. 

But should one start, straight after a person has entered Islam, with rulings on minor issues such as the beard, isbaal (letting the hem of one’s clothes come below the ankle) and so on? 

This should be based on what is referred to above, that the best of guidance is the guidance of Muhammad (blessings and peace of Allah be upon him). So he should start first of all with the basics of Islam, until Islam is settled in his heart and he is at ease in his new faith. At that point we may teach him other matters, starting with the most important, then the next most important and so on. This is the way of Allah with regard to both shar‘i rulings and laws of nature. Look how the foetus begins to grow bit by bit, and the four seasons change bit by bit, and the sun rises and sets similarly. If we were to teach all the rulings and so on all at once, it would take a long time and it may put him off the religion of Islam. End quote. 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) 

Al-Ijaabaat ‘ala As’ilat al-Jaaliyaat, 1/27-30