I really like this prayer that we can say for others. It takes the sometimes too personal element out of things (especially if we're having difficulty with the person in question) by addressing the prayer to their guardian angel.
"Spirits ever watchful, Guardians of your souls,
May your wings carry
Our souls' petitioning love
To the human beings upon Earth
Committed to your care;
That, united with your power,
Our prayer may radiate with help
To the souls whom our love is seeking."
German original:
"fuer die Freunde auf Erden, besonders diejenigen in Gefahr"
"Geister Eurer Seelen, wirkende Waechter,
Eure Schwingen moegen bringen
Unsrer Seelen bittende Liebe
Eurer Hut vertrauten Erdenmenschen;
Dass, mit Eurer Macht geeint,
Unsre Bitte helfend strahle
Den Seelen, die sie liebend sucht."
~Rudolf Steinerfrom 'Verses and Meditations pages 204/205