Prayer is intimate conversation of the nous (intellect) with God.

So then, what stable state must the nous possess to be able to stretch out unalterably toward its own Master and converse with him without any intermediary?

If Moses was hindered when he attempted to approach the bush burning on earth, until he had taken off the shoes from his feet (Exod. 3:2-5), do you not think that, if you wish to both see the One who is above every concept and perception and to converse with him, you should cast away from yourself every impassioned mental concept (noema)?

First of all pray that you may receive tears, so that by means of sorrow (penthos) you may be able to calm the wildness within your soul; and by confessing your iniquity to the Lord, obtain forgiveness from him.

Make use of tears to realize every petition, for it delights your Master to receive prayer offered with tears.

Even if you weep rivers of tears at your prayer, on no account be inwardly haughty, as if you were superior to others.

For your prayer has received this help so that you may be able to more easily confess your sins and propitiate the Lord by means of tears.

So do not turn into passion the antidote to passions, lest you anger all the more the One who gave you this grace.

[…] Stand patiently toiling, and pray well-toned, and put to flight the assaults of anxieties an [tempting thoughts: they disturb and trouble you in order to make you relax your tone.

 When the demons see that you are eager to truly pray, they insinuate mental concepts (noemata) of certain affairs that seem to demand attention.

And within a short time they arouse the memory of these things and move the nous to seek them out. And failing to find them, it becomes very sorrowful and disheartened.

Then when the nous stands for prayer, the demons remind it of the matters it had sought and remembered, so as to make it halfheartedly seek knowledge of them and thus lose the fruitfulness of prayer.

Exert your nous to stand at the time of prayer [as if] deaf and dumb, and [then] you will be able to pray.

Whenever you encounter temptation, contradiction, or yearning; or when indignation (thumos) moves you to take revenge on your opponent or to break out yelling.

Remember prayer and the judgment that attends on prayer, and immediately the unruly movement within you will be quieted.

Evagrius the Solitary (345-399): On Prayer, 3-12, translated by Luke Dysinger OSB.