The following is an excerpt from The Upper Room Dictionary of Christian Spiritual Formation; editor Keith Beasley-Topliffe:
Choose a short, "sacred word" of one or two syllables, such as love, joy, peace, Lord, Jesus, etc. This word symbolizes your intention to consent to God's presence and action within.
Sit in a comfortable position with your eyes closed.
Inwardly repeat the sacred word as a means of centering your thoughts on your yearning for God.
Whenever an emotion, image, memory, or even a spiritual communication appears, gently reintroduce the sacred word.
After twenty minutes have elapsed, return to ordinary thought by repeating the Lord's Prayer.
How do you know when twenty minutes have gone by? You could peek occasionally at a watch or clock. You could use a countdown timer, though these can be quite startling! Or you could use a recording with twenty minutes of silence followed by quiet music that fades in.