The means of developing Khushoo'
1. Striving to gain that which gives and strengthens khushoo’. This can be achieved in several ways, such as the following:
Preparing oneself for prayer properly
a. By repeating the words of the adhaan after the muezzin;
b. By pronouncing the dua to be recited after the adhaan
c. Reciting dua between the adhaan and the iqaamah;
d. Doing wudoo properly, saying Bismillaah before it and making dhikr and saying the dua after it,
e. Using siwaak to cleanse and perfume the mouth that is going to recite Quran in a short while
f. Wearing one’s best and cleanest clothes,
g. We should also prepare ourselves by covering our awrah properly, purifying the spot where we are going to pray, getting ready early and waiting for the prayer, and making the rows straight and solid, without any gaps, because the shayaateen come in through the gaps in the rows.
2. Moving at a measured pace during prayer:
The Prophet ﷺ used to move at a measured pace during salaah, allowing every bone to return to its place.
Abu Qutaadah (رضي اللّٰه عنه ) said: “The Prophet ﷺ said: “The worst type of thief is the one who steals from his prayer.” He said, “O Messenger of Allah, how can a person steal from his prayer?‟ He said, “By not doing rukoo and sujood properly.” (Reported by Ahmad and al-Haakim, 1/229; Saheeh al-Jaami‟, 997).
The one who does not move at a measured pace in his prayer cannot have khushoo because haste is a barrier to khushoo and pecking like a crow is a barrier to reward.
3. Remembering death whilst praying:
The Prophet ﷺ said: “Remember death in your prayer, for the man who remembers death during his prayer is bound to pray properly, and pray the prayer of a man who does not think that he will pray any other prayer.” (al-Silsilat al-Sahihah by al-Albaani, 1421.)
The Prophet ﷺ also advised Abu Ayub (رضي اللّٰه عنه): “When you stand up to pray, pray a farewell prayer.” (Reported by Ahmad, 5/412; Saheeh al-Jaami‟, no. 742) – meaning the prayer of one who thinks that he will not pray another prayer. The person who is praying will no doubt die, and there is some prayer that will be his last prayer, so let him have khushoo’ in the prayer that he is doing, for he does not know whether this will be his last prayer.
Source: 33 Ways of developing Khushoo' in Salaah by Sheikh Muhammed Salih Al-Munajjid