Pope Shenouda III
Train yourself to pray the repetitive short prayers:
  For example,  the prayer: “My   Lord Jesus Christ have mercy on me”, or “Make haste, O  God, to deliver me! Make  haste to help me,” or “I love the   Lord  Jesus Christ, and I bless His  name”, or “I thank you Lord on every  occasion”... or any short verse  that you make up for yourself as a  prayer and that suits your condition  and expresses your feelings... By  repeating a prayer, it makes it  register in your subconscious so it  will be in your thoughts automatically and  may stay with you, even in  your sleep. The saying of the Psalmist, “...I remember You on my bed” (Ps 63:6),  refers to this.