Following the instructions of the Church. You can find them in detail on the Vatican website. Click here for full details. All the norms are there. READ that Vatican page because, although it is long, the explanation is second to none.
In short, the key is this: to abhor all venial sin and to do the works that the Church asks of us. The difficult thing is not to do the works that the Church asks of us. The difficult thing is to abhor all sin, even venial sin. The bold is ours:
In order to gain a plenary indulgence, the performance of the work enriched with the indulgence and the fulfillment of the following three conditions are required: sacramental confession, Eucharistic communion and prayer for the intentions of the Roman Pontiff. It is also required that all affection for sin, even venial sin, be excluded.St. Paul VI, Apostolic Constitution Indulgentiarum doctrina, 1967.
That done, everything else is easy. The Church knows that's the hard part:
If this complete provision is lacking, and the above conditions are not fulfilled, except as prescribed in Rule 11 for the disabled, the indulgence will be only partial.St. Paul VI, Apostolic Constitution Indulgentiarum doctrina, 1967.
Take heart because God's mercy is infinitely greater than our sin. So, counting on that infinite mercy, the conditions for gaining a plenary indulgence are:
- Aversion to all sin, even venial.
- Eucharistic communion.
- Pray for the Pope and his intentions.
- To make the practice of piety that generates the plenary indulgence.
It is easy because it does not have to be done all on the same day, but a few days before or after the execution of the work of piety that generates the plenary indulgence:
The three conditions can be fulfilled a few days before or after the execution of the prescribed work; however, it is advisable that communion and prayer for the intentions of the Supreme Pontiff take place on the same day that the work is done.St. Paul VI, Apostolic Constitution Indulgentiarum doctrina, 1967.
Sacramental confession is valid for several days:
A single sacramental confession can gain many plenary indulgences, while a single Eucharistic communion and a single prayer for the intentions of the Supreme Pontiff can gain only one plenary indulgence.St. Paul VI, Apostolic Constitution Indulgentiarum doctrina, 1967.
One plenary indulgence can be gained each day, and only one:
The plenary indulgence can only be gained once a day, except as prescribed in norm 18 for those who are in articulo mortis.St. Paul VI, Apostolic Constitution Indulgentiarum doctrina, 1967.
Prayer for the Roman Pontiff need not be complicated:
Norm 10. The condition of praying for the intentions of the Supreme Pontiff is fully fulfilled by reciting an Our Father and a Hail Mary for his intentions; although each of the faithful may pray another prayer, according to his devotion and piety for the Roman Pontiff.St. Paul VI, Apostolic Constitution Indulgentiarum doctrina, 1967.
And what are the practices of piety that allow us to gain a plenary indulgence? There are many. You can find the general rules on the Vatican web site, or examine the list of indulgences in the web site of the Apostolic Penitentiary. You can download them HERE in pdf. You can see them here on line in Latin directly from the Vatican. But we summarize the most affordable for a normal person in their daily life:
7. Particularly noteworthy are the concessions that refer to certain works which, enriched with plenary indulgence, the Christian faithful can gain every day of the year, while Rule 21 § 1, according to which only one indulgence per day can be gained, remains in force:
- Adoration of the Blessed Sacrament for at least half an hour (no. 3).
- The pious reading of Sacred Scripture for at least half an hour (no. 50).
- The pious exercise of the Way of the Cross (No. 63).
- The recitation of the Marian rosary in a church or oratory, or in a family, in a religious community, in a pious association (no. 48).Apostolic Penitentiary, Enchiridion Indulgentiarum.
In short: if you go to confession frequently and go to Mass often, by simply praying the rosary in a church or with your family, you gain a plenary indulgence EVERY DAY. The Church cannot administer more mercifully the merits of Christ. Take advantage of it: just like the sacrifice of the Cross, it takes place in time but its dimension is ETERNAL.