How death anniversaries take place by Buddhist rituals? My loving grandma passed away on 1st April 18 so we want to have death anniversary.
So I want to ask when should we arrange ceremony, on first April or first March?
We tribute a person with chanting Refuge and  Panchashila. 
So is something missing?
Sadhu, Nyom. What ever day, is a good day to show respect toward the ancestors, to give Alms to the Sangha to benefit them, to listen to the Dhamma by your self.
Don't forget, if it had not been done in the past by your ancestors you would not ever had met the Dhamma.

Of what one should not miss when giving: Sila, virtue, what ever dedicating, is just the good given, if it does not harm others.

Invite many to take part on the merits and share them with all.

Mudita