For me, there isn't one right or wrong thing to say when it comes to grief. Honestly, what one person says in one moment may be perfectly fine and someone else could say it in exactly the same way and it would go over like a lead balloon. Is that fair? Nope. And I know that, but fair doesn't really count for me anymore.
There have also been countless times when someone has said, "I wanted to tell you that when I said that thing before, I didn't think about how it would make you feel, and I'm sorry." Here's the thing with that, I probably didn't notice. You may have said something to me that you considered thoughtless at the time, but I most likely never think about it. And if i did notice, and I do think about it, then I've probably already made my peace with it. Honestly, most of my days are spent letting difficult conversations roll off my back. I'm constantly reminding myself that not everyone has had my experiences and that things that they say aren't meant to be hurtful. Of COURSE I know you don't mean to hurt me, or to say something callous in regards to the death of my son. In the cases in which I am affected by something someone has said, I do appreciate the acknowledgement (no matter how much later you recognize it) because it validates my feelings as a grieving mother. But I don't fault you for being a normal human being. I don't wish for you to truly know my perspective.
I think, for me, the most important thing I can tell someone who is worried about what they say around me is to remember that it isn't about them. Of course my friends and family are going to talk about their children, complain about their antics, share their joyful moments. I know that! I'm a mother too. And I'll share all of those things about my children as well. All four of them. And I'm not going to stop. But some things that you say to me are going to hurt. That's just how this is going to be for me in this lifetime. It isn't your fault, and it isn't mine. As much as you can't help hurting me with the things you may sometimes say, I can't help the fact that sometimes your words hurt me. And I'm OK with that. The key is for you to be OK with that too. Don't make it the grieving person's job to make you feel better about what you say. And I don't mean that in a harsh, "I don't care about your feelings", way. I just mean that in that moment, that person is probably just trying to hold herself together. She doesn't have the capacity to make it OK for you too.
I certainly don't hold those moments against anyone. I don't know how to do grief either! I'm learning every day. And I only know how I feel. I can say that if your grieving person is anything at all like me, she'll need free reign on her emotions. Let her be positive when she wants to be positive. Let her scream and heave and sob in anger when she can't. Tell her that there is beauty in the strength to allow herself to fall apart. Let her pray to God, if she has hope in miracles. Let her denounce religion and higher power if that's where her mood takes her. I was once told I didn't have a free pass just because I "lost my child." I'm saying give her one. Love her. Let her know that all of her emotions are welcome. Not just the ones that make you feel more comfortable.
And for those of you on your own grief journey, no matter what that might mean, I wish you enough love to carry you through. It's your only guarantee.