Here’s what I wrote about prayer in another thread. Hope it’s helpful to someone:
To me, the term “mental prayer” is a distinction from “vocal prayer.”
Vocal prayers are all the prayers we all say - the Our Father, the Hail Mary, the Glory Be, the Creed, the Hail Holy Queen, the litanies, the Anima Christi, etc., etc., etc. They’re written down and formalized.
Mental prayer, on the other hand, is our personal conversation with God - we tell Him how much we love Him, how we adore Him, how sorry we are for our sins, what we’re worried about, what we’re happy about, what we’re thankful for, what we think we need, what we want for those we love and on an on. There are, as has been noted by previous posters, many “ways” of mental prayer. You can meditate on a passage of scripture, picturing yourself in the scene. You can take a vocal prayer and slowly meditate on each sentence. You can take a book of points for meditation and read until something strikes you, then take off with that. You can just chat. But make sure to spend some time also listening. A one-sided conversation with God is no better than one with anyone else. At the end of the prayer, try to form some kind of resolution about how you will carry out what you gleaned from the prayer time.
I like this little prayer to end a time of mental prayer: “I thank you, my God, for the good resolutions, affections, and inspirations You have communicated to me in this time of prayer. I beg Your help to put them into effect. My Immaculate Mother, St. Joseph, my father and lord, my guardian angel, intercede for me.” While we’re at it, here’s the matching prayer for the beginning: “My Lord and my God, I firmly believe that You are here, that You see me, that You hear me. I adore You with profound reverence. I ask pardon for my sins, and grace to make this time of prayer fruitful. My Immaculate Mother, St. Joseph, my father and lord, my guardian angel, intercede for me.”
Betsy