A few quotes from The Philokalia:
“Thoughts gather about the soul according to its underlying quality.”
“He who loves God lives the angelic life on earth, fasting and keeping vigils, praying and singing psalms and always thinking good of every man.”
“Always keep the same measure of self-control; otherwise through irregularity you will go from one extreme to another.”
“To give free reign to the senses is to shackle the soul, to shackle the senses is to liberate it.”
“Contradiction and contentiousness come from deceit, a companion of unbelief and haughtiness."
“The highly experienced and wily demon of unchastity is ... a scourge for those who have advanced midway along the path of virtue but then relax in their efforts.”
“You must also pay attention to the thoughts of arrogance and presumption which attack you ... For when the demons see the soul freed from passions and temptations, they attack it through such thoughts.”
