Anything starting with "At least." For example "At least she didn't suffer." Those two little words have a sting in them. They suggest the griever shouldn't be as sad as they are.
Avoid "How are you?" I know how easy it is for this statement to slip out but you are giving the grieving person the hard job of having to figure out an answer. They feel obliged to say "Fine" which is obviously not the case. Instead try a caring statement:
"I've been thinking about you", "I'm here for you", "It's so nice to see you." If there are tears, don't run away. Wait until it passes and ask if you can help with the shopping. If they look uncomfortable, ask: "May I call you and perhaps we could meet when you would like some company."
Avoid "God's will." I don't think this one needs further explanation…
Generally, be a sensitive, compassionate and empathetic listener looking your friend in the eye when talking. Smiling, touching and warm looks all convey affection. Three pats on the back may say, "There now, be done now" while a hand on the shoulder or arm may invite continued talking. A note of warning about being warm – it doesn't mean puppy dog pity eyes. Offer honest words of caring. Share memories. Be available to listen and less eager to relate your personal experiences or say the right thing.
Don't offer advice or talk about the people you've known who have died from the same disease.
Don't feel uncomfortable if there's a lull in the conversation. It might feel awkward, but quiet is better than empty words. Your presence shows you care.
Most importantly, work to strike the right balance. It's OK to be concerned, but not OK to be intrusive. Allow them their privacy.
Don't be afraid to ask them for guidance in how you can best help them through their challenges ahead. Remember, your commitment to being supportive to your friend in their grief is a compassionate gift.
Be willing to learn from those who grieve. Don't forget to take care of yourself.
Specific phrases to avoid:
Miscarriage: "It probably happened for the best"; "You're still young enough to try again"; "At least you have another child"; "You have your whole life ahead of you"; "Call me when I can help."
Spouse: "You're still young, you can always remarry"; "He/she led a full life"; "Death was a blessing"; "Call me when I can help."
General: "I understand how you feel"; "It was God's will"; "Something good will come out of this"; "He/she led a full life"; "Call me when I can help"; "Be strong!"