"Successful indeed are the Believers, those who offer their Prayers with khushu' (solemness and submissiveness)"
Surah al-Mu'minoon (The Believers)
Chapter 23: Verses 1,2
 

Commentary

Shaytan is after your Khushu' 

• Salah (prayer) is the greatest of the practical pillars of Islam, and khushu' (concentration and humbleness) in prayer is the heart of your worship and your relationship with Allah.
• No wonder, when Shaytan, the enemy of Allah, vowed to mislead and tempt the children of Adam ('alayhi salaam) and said, 'Then I will come to them from before them and behind them, from their right and from their left' [7:17], one of the plots he devised was to divert people from prayer by all possible means. Thus, he whispers to us during our Salah diverting our attention, depriving us of the joy, love, and sweetness of this worship, and diminishing our reward for it

• Khushu', as important as it is, is easily lost and rarely observed, especially in our present times. According to the Prophet (peace be upon him), with the passage of time, "The first thing to be lifted up from this Ummah will be khushu', until you will see no one from among you who has it." [al-Haythami, al-Tabarani]

How to Achieve Khushu' 

• Remember that khushu' comes from the heart, and only its effects are manifested in the physical body. The various faculties follow the heart. So if one's heart is corrupted by negligence or whispers from Shaytan, the worship of his body will also be corrupt.

• To perfect khushu' in prayer, one should have a conscious fear of Allah, pray in a calm and collected manner, perform every act and movement with humility and full awareness of its significance, and take time to experience the serenity and tranquility. 

• Ibn Kathir says: Khushu' in prayer is achieved when a person empties their heart for it (prayer), focuses on it and prefers it over everything else. Only then do they find comfort and joy in it.

• This is also the cure to feeling lazy, monotonous and a lack of motivation in acts of worship, since Allah says: "Verily it (the duty of prayer) is heavy, except on those who have khushu'."

[compiled from "33 Ways of Developing Khushu' in Salah" by Shaykh Salih al-Munajjid and "Salah: The State of Mind" by Young Muslims Publications ]