How can one achieve humility and devotion in prayer, and is prayer considered unacceptable if humility and devotion are not maintained throughout it?

Khushūʿ (devotional humility) is the spirit of prayer. It is a state of fear, mindfulness, and humility before God within the heart, the effect of which becomes apparent on the limbs through stillness and attentiveness to the prayer. It is something beyond mere presence of mind. To achieve it, one should earnestly supplicate to God, ponder over what is recited from the Qur'an and adhkār (remembrances), feel as if one is standing before God, stay away from distractions, and recall the sweetness of communing with God. As for the acceptance of prayer, its knowledge rests with God. However, if a Muslim performs an act of worship correctly and with sincerity to God, then God will not let his reward be lost. Acceptance is of various types: acceptance with pleasure and love, acceptance with recompense and reward, and acceptance solely to avert punishment, as in the prayer of one whose heart was not present, which fulfills the obligation but for which one is not rewarded except for what one understood from it.