Some DO's

Here, as promised, are some things and words that actually helped me.  When one you care about is deep in grief you can support them.

The biggest thing to me is not being judged!
In your interaction with a griever be unconditional.  Leave the blame/guilt game out of it.  No one knows how one's own reaction might be in a similar situation.
And it does not help to hear an opinion as to 'good or bad' ...it is neither; it just IS.

Express your honest concern.  Grief IS the elephant in the room...do not ignore it.  How sad it was for me to think that you don't care.  And how comforting to hear in your voice compassion.

Be truly available.  One hears so often "call if you need anything".  Maybe i do need something yet i don't know what.  Perhaps you could just come to me and wait while i figure it out.

Offer some very practical services. Especially if the loss was of someone very close it is easy to forget practicalities. When my husband died I was not thinking about much at all;  i was running on autopilot.
My dear, dear friend, M. E., not only lent her heart to me for hearing my pain she also provided advice and assistance in dealing with things that just have to get done.  She made a binder for me with items that needed attention and sectioned it off into "immediate", "next week", "monthly", etc.  She even made some difficult calls for me in those first few days...like dealing with the funeral home and notifying people of my spouse's death.

Last on this post though surely not least LISTEN.  Between the lines and in the silence...listen with your heart.