Before death, would include the person dying and the people around them. After death, that is just going to be the people around, as far as we know. How can beneficial mind states just before death be supported?
As far as I know, concerning after death, we can only discuss what the people around the deceased can do to possibly help the person who has just died.
While the person is dying, it can often help to talk about good inspiring, uplifting things. If you are ever around someone dying, even if they are not a meditator, can you get them to talk about the good things they did in their life? Get them to talk about something special in which they helped somebody, in which they did some charity work, something of that sort.
It's like with my mother, some years ago, she now can't do it any more, but she volunteered in a hospital once a week, four hours a day, for 20 years, donating her time. The hospital volunteer organization had over a thousand people, both retired people who were able to help during the week and younger people who came on the weekend or stay all night. She helped for 20 years.
Now every time we talk about this with her, she has feelings of happiness and joy arise, knowing that what she did was something special.
So if I am around her when she dies, that would be something I would want to remind her about so that she focuses on her good Kamma. I would want her mind to focus on that. I won't mention relatives she didn't like as that may cause aversion to arise. Whereas focusing on her charity work helps joy and happiness for herself to arise and reminds her about the compassion she had for others.
So one of the best ways to help encourage beneficial mind states to arise just before death, is to have the dying person talk about their good past actions, or you talk to them about their good past actions.
Now after death we are basically talking about the people left behind. According to Buddhism, if the people left behind express their grief with crying, going on and on, then they are not only suffering but according to Buddhism it may actually harm the person who has died. Buddhism teaches us that when a person dies, for a short time after death they may stay around their dead body.
Now if they stay around their body witnessing their relatives being overcome by grief, upset and sad, they will be affected and be pulled back, preventing them from going on to their next life, and can become stuck in a limbo state. Due to their attachment and concern for their relatives and friends, they are unable to be reborn.
Theravadin Buddhism does teach that the people left behind can help the dead person by doing some good Kamma for the person who died such as donating some money for charity in the persons name.
It is common in Thailand for the children, the wife or husband to ordain, even if it is just for a week, and dedicate the merits of what they have done to be of some benefit to the dead person.
It is also encouraged for people to wish the dead person well, and do some Compassion/Lovingkindness for the person who died, wishing them well wherever they are reborn. If the dead person sees their relatives reacting in that way, less concern will arise for them, they are content that it is ok to leave.
They can get reborn easier that way, in a normal state. So before a person dies, help them by having them or you talk with them about their good Kamma. After a person dies make some good Kamma, dedicate it for them and to also wish Compassion/Lovingkindness for the person who died, that would be very beneficial.