How can I achieve the Oneness of God (Tawhid al-Uluhiyyah), be sincere in my intention to seek Allah's pleasure, make the Hereafter my goal, and free myself from worldly desires after repeated setbacks?

Sincerity is achieved by realizing its importance and the danger of losing it. Self-admiration and showing off can be overcome by making the Hereafter one's greatest concern, by recognizing the fleeting nature of this world and the reality of the Hereafter. It is recommended to read books on spiritual refinement and matters of the heart, and to strive in supplication that the Hereafter be one's greatest concern.