I, fortunately, have yet to experience the death of a loved one. But from what I've read, you can upscale from something smaller. Such as, the loss of a pet.
But if you haven't lost your hamster, either, then online is usually the best place to look for ideas.
https://www.writerscookbook.com/how-to-write-about-grief/
There's the five stages of grief:
Denial
Anger
Bargaining
Depression
Acceptance
Another thing you can do is ask a lot of questions. Such as, does everyone go through the five stages?
Little things. All of this also depends on who the character is.
If you have any other questions, I'm always ready to help! :D