Sometimes it can be difficult to know how to pray for a friend. I found this link very helpful, it contains very wise and useful advice about this matter. (I believe this is written by Father Seraphim Holland, an American ROCOR priest).
I have found myself using this prayer that he recommends very often:
Save, O Lord, and have mercy on Thy servant(s)________
Deliver him (her, them)
from every tribulation, wrath and need,
From every sickness of soul and body,
Forgive him (her, them) every transgression, voluntary and involuntary,
And do whatever is profitable for our souls
I hope it will be useful for the readers of this blog too.