Get a group of 6 parishioners who are willing to take this on.
Have a meeting with them to explain what is involved both in getting this started and in maintaining it month by month.
Set a date for starting. This will then be the date each month for the parish
Set a date for launching it. This means a date on which someone – the priest of the parish, some of the group of 6, or a combination – would talk about this day maybe at all the weekend Masses or at some other special occasion at which a good number of people are gathered.
Have sheets available on this occasion of the launch for people to sign up, with some of the leaders there to help this to happen.
Use the time between this occasion and the beginning date, to recruit others to sign up for an hour by word of mouth or by the Parish Newsletter etc.
On the weekend before the first day of prayer have an explanatory sheet available for all the parishioners and distributed to them both as a reminder that it is starting and also as an invitation to the whole parish to pray on that day for Marriage and Family Life. This explanatory sheet will be given to the leaders before the starting date.
Each month a different, but similar sheet will be made available to the parishioners. This will contain a short reflection on some aspect of prayer or of marriage or family life. Each month the whole parish will be encouraged to take part.
Let the day bed down gradually as part of the fabric of the parish before going on to look at other things that can be done to build up marriage and the various aspects of family life.