When your mind does wander…

When your mind does wander during prayer, bring it back. When it wanders again, bring it back again. Each and every time that you read a prayer while your thoughts are wandering (and consequently you read it without attention and feeling,) then do not fail to read it again. Even if your mind wanders several times in the same place, read it again and again until you read it all the way through with understanding and feeling. In this way, you will overcome this difficulty so that the next time, perhaps, it will not come up again, or if it does return, it will be weaker.
–Saint Theophan the Recluse (1815-1894)

Distractions are normal…  

Distractions are one of the more common difficulties in prayer. They are absolutely normal and should neither surprise nor sadden us. When we realize that we have become distracted from our prayer and our thoughts are wandering, rather than getting discouraged or angry, we should simply, peacefully and gently bring our minds back to God.
–Jacques Philippe (1947-

Difficulties at prayer…

However we do mental prayer, we can be sure of encountering difficulties. Some have already been mentioned: dryness, distaste, a sense of our own worthlessness, the feeling the effort to pray is useless. The first thing to say about such difficulties is that they should not come as a surprise or cause us to worry or be upset. Not only are they inevitable, they are actually good for us. They purify our love for God and strengthen our faith.
–Jacques Philippe (1947-

Fortitude and perseverance…

And although many conflicts of diverse kinds should abound in prayer, and darkness of mind with much confusion, the devil making the soul feel that her prayer was not pleasing to God, nevertheless, she ought not to give up on account of those conflicts and shadows, but to abide firm in fortitude and long perseverance, considering that the devil so does to draw her away from prayer the mother, and God permits it to test the fortitude and constancy of that soul.
–Saint Catherine of Siena  (1347-1380)

They do not remember God…

Why is it, you ask, that one can pray for so many years with a prayer book, and still not have prayer in his heart? I think the reason is that people only spend a little time lifting themselves up to God when they complete their prayer rule, and in other times, they do not remember God. For example, they finish their morning prayers, and think that their relation to God is fulfilled by them; then the whole day passes in work, and such a person does not attend to God.
— Saint Theophan the Recluse (1815-1894)

Prayerful zeal…

However, one does not have to do many prayers. It is better to perform a small number of prayers properly than to hurry through a large number of prayers, because it is difficult to maintain the heat of prayerful zeal when they are performed to excess.
–Saint Theophan the Recluse (1815-1894)