Avoid the causes that delay and hinder response to prayer, some of them are:
1- Weakness of the prayer due to the transgression that it contains
2- Weakness of the caller in himself due to the weakness of his heart in turning to Allaah.
3- The hindrance to response could be: going beyond one of the bounds of Allaah –The exalted- such as unlawful wealth in eating, drinking, clothing, housing, income and doing an unlawful job or renting a place to dealers in unlawful goods.
So also is sins that have clouded the heart, innovations in the religion, and the heart being inattentive (of Allaah’s remembrance and commandments). It has been authentically reported from the prophet (commendations and peace of Allaah be upon him) that he said:
Nothing can avert destiny except prayer, nothing can increase lifespan except goodness (to parents) and a man would be deprived of a provision because of a sin he committed
– Reported by Tirmidhee
4- Also, one of the reasons for delayed response is impatience, losing hope and (as a result) abandoning prayer.
5- Lastly, stay away from the things that can make a wronged person curse you even if he is a disbeliever, or sinner because his sin is for himself.
Indeed, the prayer of the wronged is always accepted and it ascends the heaven as if it were a spark of fire.
So woe to the one whom the arrows of the wronged are pointed at! And may Allaah have mercy on Imam Ibnul Qayyim who said:
So great is the difference between the person who sleeps while the eyes of the people are sleepless praying for him, and the person who sleeps while the eyes of the people are sleepless cursing him”
So fear Allaah O servant of Allah! (Beware of) oppressing His slaves, low your wings for the people and avoid wronging them and don’t set your tongue loose at their honour.
From Tasheeh-Du’a by Sheikh Bakr Abu Zayd. May Allaah have mercy on him and Sheikhul Islam.