What are important things that family members and friends should do when someone is dying?

It is recommended by the prophet Muhammad (S.A.W.) to do the following:

The dying person should be asked to pronounce, “Laa ilaaha illal Lah.” (There is no God but Allah.) before death. The prophet Muhammad (S.A.W.) said: “Ask your dying fellows to pronounce, “Laa ilaaha illal Lah.” (There is no God but Allah.)” [Reported by Imams Muslim, Abu Dawood, At-Tirmithi, An-Nisa’I and Ibn Majah]

The prophet Muhammad (S.A.W.) said: “The one whose last words are “Laa Ilaaha Illal Lah.” (There is no God but Allah) will enter Paradise.” [Reported by Imams Abu Dawood]