From The Way of the Fathers - Praying With the Early Christians, by Mike Aquilina:

 

Your will should be corrected to become identified with God's will.  You must not bend God's will to suit yours.  - St Augustine

Avoid, like the plague, a clergyman who is also a businessman. - St. Jerome 

Pious exercises nourish the soul with divine thoughts. - St Basil the Great

At the moment of prayer, chase from your spirit even the simple representations of human realities and the images of all creatures. Or the imagination, being occupied with objects of less importance, will lose Him WHO is incomparably superior to them all. - St. Maximus the Confessor

If you keep your inner man full of wicked thoughts, even if you were on Golgatha, even if you were on the Mount of Olives, even if you stood on the memorial rock of the Resurrection, you will be as far away from the receiving of Christ into yourself as on e who has not even begun to confess Him. - St Gregory of Nyssa

Do not go outside, but return into yourself, for the truth dwells in the interior man. - St. Augustine

A man will despise all things present as transitory when he has securely fixed his mental gaze on those things that are immovable and eternal, and already contemplates in heart - though still in the flesh - the blessedness of his future life. - St John Cassian 

No one understands in heart...  unless he be open-minded and completely attentive. - Origen

Preparing the heart is the unlearning of the prejudices of evil converse. It is like smoothing the waxen tablet before attempting to write on it. - St Basil the Great

Because you are cleansed, you are able to perceive what is invisible to those who are not yet purified. The darkness caused by material entanglements has been removed from the eyes of your soul, and so you see the blessed vision radiant in the pure heaven of your heart. - St Gregory of Nyssa