This is not an easy thing to do, it also takes practice. That's why we reflect on death, so that we are not shocked when it happens. We understand that everyone will die. When my father died, I tried to reflect on the universality of death and reflect on his good qualities. This is so that I wasn't focusing on what I have lost, but more on how fortunate I had been to have him as my father, someone with such good qualities, and hoping that his good qualities would be supporting him in his next life. Also Compassion/Lovingkindness, so we can transform our thoughts away from what we have lost and aim them towards concern for the person who has died. It is taught that when a person dies, they may still be aware, the consciousness may still be aware, and if the consciousness is upset by others' emotions, they may be pulled back and sometimes get stuck.
There is a story a teacher told us concerning this possibility: There was an old man who wanted to give a donation to a monastery, so he started to build a kuti - that's a little hut for a monk - and the hut was finished, he was very happy, but he died and the toilet wasn't finished. The story goes that he was very upset that the toilet wasn't finished, so he hung around as a type of spirit, wanting the toilet to be finished. The teacher had a concentration practice and was able to see that this old man was hanging around, so he informed his relatives. They finished the toilets as quickly as they could, and then the teacher went into meditation and said to the spirit: "Come on, reflect on your good Kamma and go on to your next life" So apparently at that time they reflected on their good Kamma and went on into a beneficial rebirth.
With that thought in mind, when I went back and was around where my father had died, I just went around generating good wishes about his good qualities and saying, "Don't worry about us, I'll take care of it, take care of my mother, you don't have to worry about it," and reflecting on his good actions and telling him to go on. When my niece died from liver cancer, she was 27. When I arrived I took my brother and his wife up to where she had died and we did a group meditation on reflecting on her good Kamma and wishing her well on her journey. Then for a week I suggested we do a lot of chanting, because apparently my niece was influenced by me and confessed to be a Buddhist. So I did a lot of chanting and reflection on her good Kamma for a whole week, wishing her well on her journey. Reflecting about her good qualities and the development of the Paramis she did in the time up to her death. She tried to forgive everybody, have Compassion and Lovingkindness for everybody and died peacefully.