I say the St. Gertrude prayer often.
I say a slightly different version at Mass which I’ll explain below.
Eternal Father, I offer You the Most Precious Blood of Your Divine Son Jesus, in union with all the Masses said throughout the world today, for the Holy Souls in Purgatory, for sinners everywhere, and for all those for whom I pray.
I read in the Pieta prayer book that our prayers are strongest at the Consecration, so I say that prayer the moment the Chalice is lifted at Mass. I shortened it a little so that it can be said quickly (I figure the “for sinners everywhere” covers everyone including those in the Universal Church, in my home and within my family). I’ve added the “for all those for whom I pray” as a virtual intention for anyone I have prayed for, and am praying for individually. Sometimes I will add “especially n.” if there is someone in particular who needs prayers at the moment.
Anytime I pass a cemetery or roadside cross I say that prayer and add “for the souls of those buried in the cemetery” or “for the person for whom this cross was placed” in the case of the roadside cross.
I also say the prayer when I hear someone has passed away, adding the name of the individual to the prayer.
By the way, this prayer seems to be very powerful; I’ve noticed a lot of prayers answered as a result praying it at Mass. If it is that powerful for people here on earth, I can only imagine how helpful it is for the souls in Purgatory. There is a claim that 1,000 souls are released from Purgatory each time it is said; I don’t know for sure if that claim comes with Church approval; I’ll have to research that.