Here's a excerpt from my favourite book on prayer "A Call to Spiritual Reformation" by D.A. Carson. I have personally benefited from each of the ideas he presents below and commend them to you.
"Anyone who has been on the Christian way for a while knows
there are times when our private prayers run something like this: “Dear Lord, I
thank you for the opportunity of coming into your presence by the merits of
Jesus. It is a wonderful blessing to call you Father ... I wonder where I left
my car keys? [No, no! Back to business.] Heavenly Father, I began by asking
that you will watch over my family—not just in the physical sphere, but in the
moral and spiritual dimensions of our lives ... Boy, last Sunday’s sermon was
sure bad. I wonder if I’ll get that report written on time? [No, no!] Father,
give real fruitfulness to that missionary couple we support, Whatever their name
is ... Oh, my! I had almost forgotten I promised to fix my son’s bike today
...” Or am I the only Christian who has ever had problems with mental drift?
But you can do many things to stamp out daydreaming, to stifle reveries.
One of the most useful things is to vocalize your prayers.
This does not mean they have to be so loud that they become a distraction to
others, or worse, a kind of pious showing off. It simply means you articulate
your prayers, moving your lips perhaps; the energy devoted to expressing your
thoughts in words and sentences will order and discipline your mind, and help
deter meandering.
Another thing you can do is pray over the Scriptures.
Christians just setting out on the path of prayer sometimes pray for everything
they can think of, glance at their watches, and discover they have been at it
for all of three or four minutes. This experience sometimes generates feelings
of defeat, discouragement, even despair. A great way to begin to overcome this
problem is to pray through various biblical passages.
A slight variation of this plan is to adopt as models
several biblical prayers. Read them carefully, think through what they
arevsaying, and pray analogous prayers for yourself, your family, your church,
and for many others beyond your immediate circle.
Similarly, praying through the worship sections of the
better hymnals can prove immensely edifying and will certainly help you to
focus your mind and heart in one direction for a while.
Some pastors pace as they pray. One senior saint I know has
long made it his practice to pray through the Lord’s Prayer, thinking through
the implications of each petition as he goes, and organizing his prayers around
those implications. Many others make prayer lists of various sorts…
This may be part of the discipline of what has come to be
called ‘journalling’. At many periods in the history of the church, spiritually
mature and disciplined Christians have kept what might be called spiritual
journals. The real value of journalling, I think, is severalfold: (a) It
enforces a change of pace, a slowing down. It ensures time for prayer. If you
are writing your prayers, you are not daydreaming. (b) It fosters self-examination. It is an old truism that
only the examined life is worth living. If you do not take time to examine your
own heart, mind and conscience from time to time, in the light of God’s Word,
and deal with what you find, you will become encrusted with the barnacles of
destructive self-righteousness. (c) It ensures quiet articulation both of your
spiritual direction and of your prayers, and this in turn fosters
self-examination and therefore growth. Thus, journalling impedes mental drift.
But this is only one of many spiritual disciplines. The danger in this one, as
in all of them, is that the person who is formally conforming to such a regime
may delude himself or herself into thinking that the discipline is an end in
itself, or ensures one of an exalted place in the heavenlies."
D.A. Carson, “Lessons from the School of Prayer” A Call
to Spiritual Reformation: Priorities from Paul and His Prayers. Grand
Rapids: Baker, 2006. Pg.20-22