In the course of my vocation there have been certain formal prayers I have come to use, having made them up not on purpose but just from repetition and refinement. One that is part of my regular life now is my prayer with ministers before Mass:
we pray that you pour out your Spirit on us
and make us into ministers after your own Heart.
Help us to offer this Mass to you and for your people
with gentleness and joy
so that we might be some small mirror of your Love for the world.
We make this prayer through Christ the Lord.
I never sat down and made up this prayer; it just formed itself over time in the course of wanting to pray with servers, lectors, and extraordinary ministers of Holy Communion before Sunday Mass.
Another example is my prayer to St. Joseph before driving.