To gain a partial indulgence, a Catholic in good standing must simply perform the prescribed work -- in this case make the Way of the Cross -- in the state of grace (that is, free of having committed a mortal sin that remains unforgiven in Confession) and have at least a general intention of gaining indulgences. A partial indulgence can be aquired more than once a day, unless otherwise expressly indicated.

To gain a plenary indulgence, however, several additional factors must also be present. All together, they are the following:

  1. The person must be a Catholic, not excommunicated, and in the state of grace, that is, free from mortal sin that has not been confessed and forgiven in the Sacrament of Penance.
  2. The recipient must go to Confession, receive Holy Communion, and say at least one Our Father and one Hail Mary for the intentions of the Sovereign Pontiff.  These can all be done several days before or after performing the prescribed "work," in this case, making the Way of the Cross. But it is more fitting that the Communion and the prayers for the Pope's intentions be on the same day that the "work" is performed. A single Confession suffices for gaining several plenary indulgences, but sacramental Communion must be received and prayer for the intention of the Sovereign Pontiff must be recited for the gaining of each plenary indulgence.
  3. The recipient must be free from all attachment to sin, even venial sin.  Although a person might still sin, as we all do, or even be inclined to an habitual sin, such as using God's name in vain, yet so long as the attachment to the sin or the desire to commit it is absent from the person's soul, he or she would be considered "free from attachment to sin."  (If this disposition is in any way less than perfect or if any of the prescribed three conditions are not fulfilled, the indulgence will be only partial.)
  4. Only one plenary indulgence may be gained per day.  But one can obtain the plenary indulgence "for the moment of death;" even if another plenary indulgence had been acquired on the same day.
  5. The person must perform the prescribcd work, in this case, make the Way of the Cross -- with at least the general intention of gaining indulgences.  In making the Way of the Cross, the following norms apply:
    1. The pious exercise must be made before stations of the Way of the Cross legitimately erected.
    2. For the erection of the Way of the Cross, fourteen crosses are required, to which it is customary to add fourteen pictures or images, which represent the stations of Jerusalem.
    3. Although according to the more common practice the pious exercise consists of fourteen pious readings to which some vocal prayers are added, yet nothing more is required than a pious meditation on the Passion and Death of the Lord, which need not be a particular consideration of the individual mysteries of the stations.
    4. A movement from one station to the next is required, but if the pious exercise is made publicly and if it is not possible for all taking part to go in an orderly way from station to station, it suffices if at least the one conducting the exercise goes from station to station, the others remaining in their places.
    5. Those who are "impeded" can gain the same indulgence if they spend at least a half hour in pious reading and meditation on the Passion and Death of Our Lord Jesus Christ.*

* The above was taken from the Enchiridion of Indulgences -- Norms and Grants, authorized English Edition, translated by Fr. William T. Barry, C.SS.R., Catholic Book Publishing Co., New York, New York, from the Second Revised Edition of the Enchiridion of Indulgences issued by the Sacred Apostolic Penitentiary, 1968 and originally published by Libreria Editrice Vaticana, Vatican City, 1968.