Easier said than done...

It seems to me that the person who is about to come to prayer should withdraw for a little and prepare himself, and so become more attentive and active for the whole of his prayer. He should cast away all temptation and troubling thoughts and remind himself so far as he is able of the Majesty whom he approaches, and that it is impious to approach Him carelessly, sluggishly, and disdainfully; and he should put away all extraneous things.

This is how he should come to prayer, stretching out his soul, as it were, instead of his hands, straining his mind toward God instead of his eyes, raising his governing reason from the ground and standing it before the Lord of all instead of standing.

All malice toward any one of those who seem to have wronged him he should put away as far as any one would wish God to put away His malice toward him, if he had wronged and sinned against many of his neighbors or had done anything whatever he was conscious of being against right reason.

On Prayer
Origen of Alexandria