World Youth Day 2008 Central, EWTN posted the instructions for gaining an indulgence:
Plenary Indulgence for World Youth Day 2008
Cardinal James Francis Stafford
The plenary indulgence is granted to the faithful who, on the occasion of the "Twenty-third World Youth Day", will gather at Sydney in the spirit of pilgrimage; all those who, wherever they are, will pray for the spiritual goals of this Meeting and for its happy outcome can also gain the partial indulgence.
The Youth Meeting held in the year 2005 in Cologne, offered the Apostolic Penitentiary an opportune occasion, with the authority of the Supreme Pontiff, to open wide to youth the spiritual treasures of the Church, with the aim of gathering singular fruits of sanctification.
Hence, this year, from 15 to 20 July, in Sydney, "in the great southern land of the Holy Spirit" (according to the expression of John Paul II), will celebrate the "Twenty-third World Youth Day", with the theme: "You will receive power when the Holy Spirit has come upon you; and you will be my witnesses" (Acts 1:8).
Indeed, young people gathered around the Vicar of Christ will participate in the sacred functions and above all have recourse to the Sacraments of Reconciliation and the Eucharist. In the Sacraments received with a sincere and humble heart, they will earnestly desire to strengthen themselves in the Spirit, and, confirmed by the Chrism of salvation, will openly witness the Faith before others even to the ends of the earth. May God grant that the very presence of the Supreme Pontiff among the young people gathered in Sydney express and render it such.
During the Audience the Holy Father granted to the undersigned on 21 June, the Supreme Pontiff has expressly confirmed to the Apostolic Penitentiary the special faculty to declare, through the present Decree, the bestowal of the gift of the Indulgence as follows:
The Plenary Indulgence is granted to the faithful who will devotedly participate at some sacred function or pious exercise taking place during the "Twenty-third World Youth Day", including its solemn conclusion, so that, having received the Sacrament of Reconciliation and being truly repentant, they receive Holy Communion and devoutly pray according to the intentions of His Holiness.
The Partial Indulgence is granted to the faithful, wherever they are during the above-mentioned meeting, if, at least with a contrite spirit, they will raise their prayer to God the Holy Spirit, so that young people are drawn to charity and given the strength to proclaim the Gospel with their life.