In the early days, when I felt completely out of control in a grief storm, the one thing that helped even when nothing else would was the mantra "Not my will, Lord, but Thine" -- over and over again until I calmed down. In the last few months, I've continued to pray that mantra as well as a variation on the metta: "May he be safe, may he be healed, may he find peace." Focusing on the words, trying my best to mean them, eventually brings me a deep sense of comfort.
One other thing: possibly the most helpful thing anyone has said to me was very, very early, when the dear mother of a friend put her hands on my shoulders and said "Sweet Prism, God just has a different path for you than you thought, that's all." What an amazingly wise frame! If you believe, if you trust, at some level you have to say, "Ok, God. I'm terrified, I sure don't understand, but I trust You. Show me the way."