Hazrat Moulana Ashraf Ali Thaanwi (rahimahullah) once mentioned the following:
Khushoo’ (i.e. concentration and devotion) is the rooh (soul) of salaah. The Mashaayikh have written many different ways through which one may acquire khushoo’ in his salaah.
However, through experience, it is witnessed that when a person exerts his mind very hard in trying to acquire the desired level of concentration and devotion in salaah, one becomes tired, and thereafter one loses hope and interest (as one feels it very difficult to acquire the desired level of khushoo’ in salaah).
It is for this reason that one should utilize one’s mind moderately in trying to acquire khushoo’ in salaah. The extent to which one should utilize one’s mind is that while reciting the words, one should keep his mind on the words and should not merely recite from memory (without thinking of the words).
One should recite like how a weak haafiz who is trying to memorize the Quraan Majeed recites each word in the manner that his mind and attention is on each word while reciting.
While adopting this method, if at any point one loses concentration, then he should not become grieved over the fact that his mind had drifted, nor should he become concerned about trying to not lose concentration in the future, but rather he should immediately bring his mind back to the recitation and try to keep his mind once again on the words while reciting.
(Malfoozaat Hakeemul Ummat 24/131)
Source: Ihyaauddeen.co.za