How can the sweetness of certainty be found in the heart when supplicating, and what is the way to make it steadfast?

Among the etiquettes of supplication (du'a') is for the servant to supplicate with certainty of being answered and with a good opinion of Allah. This certainty is aided by recalling Allah's appropriate names and attributes, and by recalling the vastness of His generosity and bounty. Likewise, performing good deeds and refraining from evil deeds, and observing the conditions of supplication such as having a present heart and seizing opportune times, places, and virtuous states.