Pastor Ronald F. Marshall of the First Lutheran Church of West Seattle wrote a helpful column (Seattle Post Intelligencer, Sept. 5, 1998) on correct interpretation of the Bible. He called it "Reading the Bible Backward," which means that we should interpret the Old Testament in light of the New Testament. He gives a couple of examples: The Old Testament (Leviticus 11:7) says we shouldn't eat pork, but the New Testament (Acts 10:15) says we are allowed to eat all types of food. On the other hand, the Old Testament prohibition of homosexual activity (Leviticus 25:36) is reaffirmed in the New Testament (Romans 1:27).
Pastor Marshall notes that this rule of interpretation was used from the earliest times in the Church. He quotes from St. Irenaeus (140-202 A.D.) that when the Old Testament is read by Christians it will become a "treasure hidden in the field but revealed by the cross of Christ." (Against Heresies 4:26). You will find this principle stated very concisely in the Catechism of the Catholic Church (no.129). In fact, I recommend to you the entire section on the Inspiration and Interpretation of the Sacred Scriptures (nos. 101-141).