The Laws of Prayer (The morning services) (36)

1. Even when a person concentrates properly during prayers, one should not think that because of this it is correct that Hashem should fulfil his request, for on the contrary, this reminds us of the sins of that person, for they check his deeds to see if actually he is fitting that they should listen to his prayer. Instead, they should concentrate on the idea that Hashem, in His great kindness, should be kind to him. (Shulchan Aruch and Mishne Berurah 98)

2. A person should think in his heart, “Who am I that I should come to ask for things from Hashem, if not for the great abundance of kindness with which He conducts Himself in relation to the creations?”.