That booklet makes me think I should pray only for those souls in purgatory, yet I feel that I should keep my prayer intentions varied for the time being as I am still in my infancy in the faith. There is more that I do not know that I do not know, than that which I know to look for and learn (hope that makes sense).
You can become a saint by praying just for the souls in purgatory if you do it enough. There are beautiful stories of saints who became saints by doing just that.
You might want to add the souls in purgatory to your Morning Offering. If you currently are not praying your Morning Offering, you can start right now. To be said asap every morning, even before getting out of bed. Here is an example:
"O Jesus, through the Immaculate Heart of Mary, I offer Thee all of my prayers, works, joys and sufferings of this day, for (here is where we add all of our intentions for this day) .....
all the intentions of Thy Sacred Heart, in union with the Holy Sacrifice of the Mass throughout the world, in reparation for all my sins, for the good intentions and conversion of all my relatives and associates, and in particular for the conversion of our Holy Father the pope, for the conversion of (add all the names you want), for all of the poor holy suffering souls in purgatory, especially (add all the names you want), that Thou wouldst deliver me and (those I love) from a sudden and unprovided death, that Thou wouldst please provide for me the grace of final perseverance and a happy death when it comes my turn, for a good holy Roman Catholic priest to give me the sacrament of Extreme Unction, and all the last blessings of the Church before I die, while I am still conscious and of sound mind, so that I may receive them with the proper disposition so as to completely avoid purgatory and go immediately to heaven with Thee when I die. Amen."
You can add whatever other intentions you want and make this prayer a mile long if you want, i.e. you can add or substitute whatever suits you, for example, you can say: "for the grace of humility", "to grow in the faith", "for our president", etc.
The cool thing is that when you pray the above Morning Offering, every prayer, good work etc., during that day will automatically include all of the intentions you mentioned above - in addition to whatever other intentions you might have at the time. It's too easy to not do.
By the same token, look at all the graces and favor lost by not praying your Morning Offering.