Sometimes when I don't know what to pray, I'll default to saying the Creed, an Our Father & the Acts of Faith, Hope & Charity interspersed with a few Hail Marys. I'll end with a Glory Be, but strangely, that's never the end. By that time, I have some things to say. Sometimes I'll continue reading through & praying the prayers of Thomas Aquinas, Augustine & the like.
I got to thinking today about the communion of saints & how their intercession might fit into this practice of praying "canned prayers". When certain ones penned their prayers so long ago, it was probably a result of an actual prayer time, not just a contrived writing session. As I pray these words hundreds of years later, I've come to imagine that we're praying together... As I repeat their words, its as time between us disappears. They are no longer praying for themselves, by themselves; they're interceding with me as well. I am joining with them in their prayers & they, in mine. I've found that canned prayers prove themselves to be more effective than my own at times. Afterall, "The prayer of a righteous man avails much... " James 5:16