Don't: They are in a better place.
Not everyone believes that our loved ones go on to exist in an afterlife of some sort. And while your intentions are the best, this could upset someone even more by making them feel as if they aren't 'allowed' to grieve because their loved ones are better off.
Don't: You need to move on.
Don't give someone a timeline for their grief. It could take weeks, months, or years to truly feel at peace with something. The grief will never truly leave you, you will just be better equipped to deal with it.
Don't: Time heals all wounds.
Right now it may feel as if they will never smile again. They probably can't imagine making it through this day, much less a year.
Don't: You can still talk to them, they will hear.
But they can't talk back...which is why they feel this way.
Don't: At least you had the time that you did.
It wasn't long enough. It will never feel as if it were enough. At least not now.
Don't: I know how you feel.
Even if you have been through a similar situation, each person's feelings are different.
Don't: They wouldn't want you to be sad.
Probably not, but if the roles were reversed I bet they would be pretty upset, too.
Don't: There's a reason for everything.
No matter what you believe, no reason will seem good enough to take our loved one away.
Do: I am here with you.
Just knowing that you are by their side will help them immensely. Even if it doesn't seem like it, you are appreciated.
Do: There is no good reason for why this is happened and I am sorry that it happened.
This is what someone needs to hear. That it just isn't fair.
Do: You don't have to be OK. You can let it out to me.
It's important to feel as if they can let you know how they truly feel. They are probably putting on a brave face for everyone else. Let them know they don't have to for you.