Beginning with the name of Allah – in the name of – the Most Gracious, the Most Merciful.
It is learned from Hz.Abdullah bin Abbas (R.A) that Prophet Mohammed ( Peace be upon them) stated that a person in the Grave is in similar in state to the person who is drowning in the sea and crying for help.
This person in the grave awaits in the grave for someone like his parents or brothers, sisters or friends to send blessed prayers (Fathia ), Prayers of Forgiveness or Contibute to Chariable & noble causes to Humanity on behalf of him/her so they gains blessings (Essal-e-Sawaab) in the grave.
The people in the world , When they pray for the deceased, Allah send’s great supreme blessings and forgiveness to the deceased individual(s). The blessings amount to size of mountains.
When the deceased individual receives these prayers he/she becomes more affectionate to the person(s) praying for them than the world he left. The Deceased becomes grateful, Happier, Joyful since he was remembered, thought of, in time of need.
Therefore, for the deceased the best gift from the Worldly people is to send them Prayers of Forgiveness.
Please when doing Esaal-e-Sawwab ( Coveying prayers to the Deceased) Mention specific individual(s) in your prayers but also importantly do not forget the whole of mankind! This way more people get the blessings. These blessings are not divided up . Each individual receives the same out as the first.
It is very important you pray for the whole mankind since their are people that have deceased and have no-one to pray for them for one reason or another.