To simply put it, it is the complete and most perfect way of living out our baptismal promises in imitating Our Lord. He came to us through a mother and so we go to him through Mother Church at Baptism and then Mother Mary through our consecrations.
The Preparation is broken up into four parts. The first part is getting rid of sin and the spirit of the world. Sin is what keeps us from unity with God (the entire point of our baptism and of the Church). Only once we decide to get rid of sin, can we then begin to know ourselves. This is the second part. We look at and meditate on the gifts and blessing God has given us and what we have done with them. This leads to self knowledge. The more we can get to know ourselves (our true selves seperated from sin, because sin always dehumanizes us), the more we will realize our need for God and the saint He has called us to be. This leads us to the third part which is meditations on Mary, the greatest saint that ever was or will be. She is the perfect model for union with Christ because there was never a time when she did not live this union. She never sinned and thus stayed in perfect harmony with God her entire life and now in eternity. We look for her virtues and intercession. Finally, as Mary always does, she points to Christ. She brings us to the final part of the preparation, meditations on Jesus Christ who is the reason for our consecration. He is the reason for our Baptism (we are baptized into His mystical body) and the only way we can fulfill it. After this we make our consecration; this should become a way of life to achieve holiness, a perfect relationship with Christ and his the fulfillment of our Baptismal vows. Hope this helps.