Don’t put the apostrophe in the wrong place (it’s a singular mother’s day).
Don’t buy cards or flowers (it’s supposed to be holy, not commercial).
Don’t name anything “Mother’s Day” (she owns the trademark). And thank her for those Sunday brunches every year, since she decided to make the holyday the “second Sunday in May” (the quotes are because she owns that trademark too), not May 9, the actual date her mother died.
She was quite a martinet, that Anna Jarvis, though I guess you had to be to create your very own holyday in 1908, before women were even allowed to vote.
But no one ever celebrated Mother’s Day for her – she died, childless, blind and broke in a Pennsylvania mental hospital.