The invocation is made as follows: having become aware that you are in the presence of God, cast yourself down with profound reverence. Acknowledge that you are most unworthy to remain before such a supreme Lord. Yet, knowing that his Goodness desires it, ask him for the grace to serve and adore him well in this meditation.
You may use, if you wish, some short and fervent words, like these of David: Do not cast me away, my God, from your face, and do not take from the favour of your Holy Spirit (Ps. 51:11). Let your face shine on your servant (Ps. 31:16), and I will see your wonders (Ps. 119:18). Give me understanding and I will consider your law, and keep it with my whole heart (Ps. 119:34). I am your servant, give me understanding (Ps. 119:125), and similar words.
It will be of help to pray to your Guardian Angel and the holy persons who are associated with the mystery on which you are meditating. For example, if it is death of the Lord, you could pray to our Lady, St. John, St. Mary Magdalene and the Good Thief, to share with you the experiences of heart and mind that they had at that time. If the meditation is on your own death, you could pray to your Guardian Angel, who will be with you then, to inspire you with suitable reflections, and so on for other mysteries.