He never fails to write to his mother every week.
He never fails to write to his mother every day.
He never fails write to his parents once a month.
He writes to his mother every now and then.
He writes to his mother every now and then.
I never fail to write to my parents every month.
I never fail to write to my mother once a month.
He never fails to write to his mother every week.
He never fails to write to her every week.
I make a point of writing to my mother once a month.