Sounds impossible really - to be humble we must view our a'maal as unacceptably inferior, but then at the same time be careful that this attitude does not spill over into ingratitude - ingratitude for the favour that Allah conferred on us by guiding us to perform such a'maal in the first place.
The solution to this quandary is to be found in one of Maulana Ashraf Ali Thanavi's malfoozhat - a collection of his day-to-day sayings - in which, after reprimanding a certain guest who had delusions of grandeur, he goes on to say
'And now there is this malady which many people are falling into - perceiving themselves as very pious and saintly but I say who would think such a thing when they have no way of knowing what state they will find themselves in when they die? On what virtuousness do they take pride in? Allah protect us from such thinking.
What is there to be arrogant about when in all likelihood we cannot pick out one ra'kaat from our entire life that can be said to match up to the standards expected by Allah and then these paltry offerings themselves are also by dint of His favour and His blessing otherwise we could not even execute this'
(malfooz 211, pg 169, Malfoozhat Hakeem-ul-Ummat, [Al-ifhadhat al yawmia...], Published Idara Taaleefat-e-Ashrafia)
In this short excerpt, Maulana Thanawi demonstrates this very quality - though acknowledgeing the imperfectness of our a'maal (as a prerequisite to modesty) he does not fail to mention that we are fortunate to have them anyway, fortunate to have Allah guide us to them and should value them as undeserved gifts from Allah.