Before you sit down to pray, St. Francis de Sales suggests doing this.
St. Francis de Sales was a masterful spiritual writer during the 17th century and wrote a very practical book on the spiritual life, called Introduction to the Devout Life. Instead of writing it for monks and nuns, de Sales wrote it for ordinary lay people and sought to help them in their everyday spirituality. Countless souls have found this book helpful and return to it for guidance during times of difficulty.
Here are several useful quotes from this inspiring book, in which de Sales details how to place yourself in the presence of God.
And in order to place yourself in the Presence of God, I will suggest four chief considerations which you can use at first.
First, a lively earnest realization that His Presence is universal; that is to say, that He is everywhere, and in all, and that there is no place, nothing in the world, devoid of His Most Holy Presence, so that, even as birds on the wing meet the air continually, we, let us go where we will, meet with that Presence always and everywhere.
The second way of placing yourself in this Sacred Presence is to call to mind that God is not only present in the place where you are, but that He is very specially present in your heart and mind, which He kindles and inspires with His Holy Presence, abiding there as Heart of your heart, Spirit of your spirit.
The third way is to dwell upon the thought of our Lord, Who in His Ascended Humanity looks down upon all men, but most particularly on all Christians, because they are His children; above all, on those who pray, over whose doings He keeps watch. Nor is this any mere imagination, it is very truth, and although we see Him not, He is looking down upon us.
The fourth way is simply to exercise your ordinary imagination, picturing the Savior to yourself in His Sacred Humanity as if He were beside you just as we are wont to think of our friends, and fancy that we see or hear them at our side.
Make use of one or other of these methods for placing yourself in the Presence of God before you begin to pray;—do not try to use them all at once, but take one at a time, and that briefly and simply.