Mental prayer is a method of meditating and conversing with the Lord in the interior of your heart.
It is not a complicated prayer, but it is so essential that St. Alphonsus Ligouri said, “It is morally impossible for him who neglects meditation to live without sin.”
Below is a method of mental prayer created for us by St. Alphonsus Ligouri.2
Order of Prayers
My God, I believe that You are here present, and I adore You with all my heart. I deserve at this moment to be burning in hell for my sins; O my God, I am sorry for having offended You; pardon me. Eternal Father, grant me light in this meditation, that I may profit by it.
Glory Be (for St. Joseph, your Patron Saints and your Guardian Angel)
Read a passage of scripture or other spiritual reading.
Stop at those passages that touches you. St. Francis de Sales says that, just as bees stop on flowers that provide necter, we should stop on passages that give us nourishment. Listen to God speaking to you.
Now, respond to God. The profit of mental prayer lies in how you respond to God. Tell Him that you believe in Him, are grateful to Him, love Him, are sorry for your sins and that you will do better.
Make petitions to God to become more holy, to pray more often and to execute God’s will more perfectly. Make petitions for the conversion of sinners and the relief of the souls in Purgatory.
Make a resolution to avoid a particular sin which you often commit.