How can one overcome obsessive thoughts and achieve sincerity of intention and truthfulness with Allah in all matters of life?

Satanic whispers (waswās) and evil thoughts can be overcome by: 1. Seeking refuge in Allah from Satan, the accursed, and resorting to Him, and maintaining the prescribed adhkar (remembrances). 2. Repelling whispers and thoughts and not dwelling on them. 3. Accompanying righteous people and occupying oneself with the remembrance of Allah, reciting the Qur'an, prayer, and acts of piety. 4. Seeking knowledge and occupying oneself with it, and restraining the self from desires while observing the limits set by Allah.

For a servant to be sincere in their actions for Allah and truthful with Him: 1. Matching one's words with one's actions, seeking reward, and desiring the Face of Allah and the Hereafter. 2. Avoiding innovations (bid'ah) and associating with their practitioners, and adhering to the Sunnah and associating with its adherents. 3. Purifying the soul from polytheism (shirk), showing off (riya'), seeking reputation (sum'ah), and cultivating detachment from worldly life (zuhd). 4. Being truthful in the resolve to do good, and ensuring that one's food and clothing are from lawful sources. 5. Loving good for Muslims and hating evil for them, and realizing that one's prayer, sacrifices, life, and death are all for Allah, Lord of the worlds. 6. Studying the biographies of the righteous and emulating them.