According to the view that holds one accountable for heedlessness and negligence regarding sincerity, how can one always achieve presence of sincerity in acts of worship?

In the words of the scholars, 'intention' (niyyah) has two meanings: distinguishing acts of worship from customary acts, and distinguishing some acts of worship from others—this is what the jurists (fuqaha') mean by it. The second meaning is sincerity (ikhlas), which is the intention of seeking Allah's Countenance through the action—this is what the theologians ('ulama' al-'aqidah) mean by it. Cultivating sincerity in worship means that the worshipper remains mindful that his purpose in worship, from beginning to end, is to attain Allah's pleasure and reward. This is achieved by the servant striving to focus his heart completely on the act of worship, being present in it, and not being preoccupied with anything else.