[1]Offer condolences to the bereaved — "Inna lillahi wa inna ilayhi raji'un."
[1]Say: "May Allah forgive your deceased and give you patience and reward."
[2]Prepare food for the family of the deceased — the Prophet ordered this for Ja'far's family. (Abu Dawud 3123)
[2]Visit the bereaved within 3 days ideally.
[1]Make du'a for the deceased and their family.